Ambient light determination using physiological metric sensor data

ABSTRACT

A wearable computing device includes an electronic display with a configurable brightness level setting, a physiological metric sensor system including a light source configured to direct light into tissue of a user wearing the wearable computing device and a light detector configured to detect light from the light source that reflects back from the user. The device may further include control circuitry configured to activate the light source during a first period, generate a first light detector signal indicating a first amount of light detected by the light detector during the first period, deactivate the light source during a second period, generate a second light detector signal indicating a second amount of light detected by the light detector during the second period, generate a physiological metric based at least in part on the first light detector signal and the second light detector signal, and modify the configurable brightness level setting based on the second light detector signal.

PRIORITY CLAIM

This application is a continuation of U.S. application Ser. No.15/828,209 filed on Nov. 30, 2017, entitled AMBIENT LIGHT DETERMINATIONUSING PHYSIOLOGICAL METRIC SENSOR DATA, which is a continuation-in-partof U.S. application Ser. No. 15/436,440 filed Feb. 17, 2017, issued asU.S. Pat. No. 10,209,365, entitled GPS POWER CONSERVATION USINGENVIRONMENTAL DATA, which is a continuation of U.S. application Ser. No.14/940,072 entitled GPS POWER CONSERVATION USING ENVIRONMENTAL DATA,filed on Nov. 12, 2015, issued as U.S. Pat. No. 9,572,533, which is acontinuation of U.S. application Ser. No. 14/700,069 entitled GPS POWERCONSERVATION USING ENVIRONMENTAL DATA, filed on Apr. 29, 2015, issued asU.S. Pat. No. 9,198,604, which is a continuation of U.S. applicationSer. No. 14/290,909 entitled GPS POWER CONSERVATION USING ENVIRONMENTALDATA filed on May 29, 2014, issued as U.S. Pat. No. 9,044,171, U.S.application Ser. No. 14/290,909 claims the benefit of priority under 35U.S.C. § 119(e) to U.S. Provisional Patent Application Nos. 61/973,614entitled GPS ACCURACY REFINEMENT USING EXTERNAL SENSORS filed Apr. 1,2014, 61/955,045 entitled GPS POWER CONSERVATION USING ENVIRONMENTALDATA filed on Mar. 18, 2014, 61/946,439 entitled HEART RATE DATACOLLECTION filed on Feb. 28, 2014, and 61/830,600 entitled PORTABLEMONITORING DEVICES AND METHODS OF OPERATING SAME, filed on Jun. 3, 2013.U.S. application Ser. No. 15/828,209 filed on Nov. 30, 2017, entitledAMBIENT LIGHT DETERMINATION USING PHYSIOLOGICAL METRIC SENSOR DATA, is acontinuation-in-part of U.S. application Ser. No. 15/436,440, U.S.application Ser. No. 13/924,784 entitled PORTABLE BIOMETRIC MONITORINGDEVICES AND METHODS OF OPERATING SAME filed on Jun. 24, 2013, issued asU.S. Pat. No. 8,954,135; U.S. application Ser. No. 13/924,784 claims thebenefit of priority under 35 U.S.C. § 119(e) to U.S. ProvisionalApplication Ser. No. 61/752,826 entitled PORTABLE BIOMETRIC MONITORINGDEVICES AND METHODS OF OPERATING SAME filed on Jan. 15, 2013 and61/662,961 entitled WIRELESS PERSONAL BIOMETRICS MONITOR filed on Jun.22, 2012. U.S. application Ser. No. 15/828,209 also claims the benefitof priority under 35 U.S.C. § 119(e) to U.S. Provisional ApplicationSer. No. 62/428,158 filed Nov. 30, 2016 entitled AMBIENT LIGHTDETERMINATION USING PHYSIOLOGICAL METRIC SENSOR DATA. The entirety ofthe above herein incorporated by reference.

BACKGROUND Field

The present disclosure generally relates to the field of wearableelectronic devices.

Description of Related Art

Wearable electronic devices can generate and/or provide informationrelated to physiological metrics associated with a user. Information maybe presented to the user through the use of an electronic display thatis illuminated using a display illumination component.

SUMMARY

In some implementations, the present disclosure relates to a wearablecomputing device comprising an electronic display with a configurablebrightness level setting, a physiological metric sensor system includinga light source configured to direct light into tissue of a user when theuser is wearing the wearable computing device and a light detectorconfigured to detect light from the light source that reflects back fromthe user, and control circuitry. The control circuitry is configured toactivate the light source during a first period, generate a first lightdetector signal indicating a first amount of light detected by the lightdetector during the first period, deactivate the light source during asecond period, generate a second light detector signal indicating asecond amount of light detected by the light detector during the secondperiod, generate a physiological metric based at least in part on thefirst light detector signal and the second light detector signal, andmodify the configurable brightness level setting based at least in parton the second light detector signal.

The control circuitry may be further configured to determine one or morephysiological characteristics of the user, adjust one or moreillumination parameters of the light source based on the determined oneor more physiological characteristics and adjust one or more receptionparameters of the light detector based on the determined one or morephysiological characteristics.

In some embodiments, the control circuitry is further configured toadjust the one or more reception parameters of the light detector beforegenerating the second light detector signal. The control circuitry maybe further configured to adjust the one or more illumination parametersand to adjust the one or more reception parameters before activating thelight source during the first period.

The control circuitry may be configured to generate the physiologicalmetric at least in part by partially cancelling an effect of ambientlight on the first light detector signal. For example, cancelling theeffect of ambient light on the first light detector signal may involvesubtracting out the second amount of light from the first amount oflight. In certain embodiments, the control circuitry is configured togenerate the first light detector signal and the second light detectorsignal using a transimpedance amplifier coupled to sample-and-holdcircuitry. The electronic display may be associated with a first (e.g.,front) side of the wearable computing device and the light source andlight detector may be associated with a second (e.g., back) side of thewearable computing device.

Modifying the configurable brightness level setting may involve changingthe configurable brightness level setting from a first mode to a secondmode. In certain embodiments, the first mode corresponds to an outdoorlighting condition and the second mode corresponds to an indoor lightingcondition. In certain embodiments, the first mode corresponds to anindoor lighting condition and the second mode corresponds to an outdoorlighting condition. The second mode may be associated with a relativelyhigher brightness compared to the first mode. Alternatively, the secondmode may be associated with a relatively lower brightness compared tothe first mode. The control circuitry may be further configured to lockthe configurable brightness level setting of the electronic display inthe second mode until the electronic display is powered down. In certainembodiments, the first mode and the second mode are a subset of a groupof three or more operational brightness modes for the electronicdisplay.

In certain embodiments, the light source comprises a plurality of LEDlight sources. In certain embodiments, the control circuitry is furtherconfigured to determine whether an amplitude of the second lightdetector signal is greater than a threshold value, wherein saidmodifying the configurable brightness level setting is based at least inpart on said determination.

In some implementations, the present disclosure relates to a biometricmonitoring device comprising an electronic display associated with afirst (e.g., front) side of the biometric monitoring device, theelectronic display having a configurable brightness level setting, and aphysiological metric sensor system including a light source and a lightdetector associated with a second (e.g., back) side of the biometricmonitoring device. The physiological metric sensor system is configuredto generate a physiological metric signal at least in part by directinglight from the light source into a user during a first period of time,detecting a first amount of light during the first period of time, thefirst amount of light including reflected light from the light sourceand first ambient light, detecting a second amount of light during asecond period of time using the light detector, the second amount oflight including second ambient light, and at least partially cancellingthe first ambient light in the first amount of light based on the secondamount of light. The biometric monitoring device further comprisescontrol circuitry configured to adjust the configurable brightness levelsetting of the electronic display based at least in part on the secondamount of light.

The physiological metric sensor system may be configured to generate thephysiological metric signal substantially continuously. In certainembodiments, the second period of time occurs temporally before thefirst period of time.

In some embodiments, the control circuitry of the biometric monitoringdevice is further configured to determine one or more physiologicalcharacteristics of the user, adjust one or more illumination parametersof the light source based on the determined one or more physiologicalcharacteristics and adjust one or more reception parameters of the lightdetector based on the determined one or more physiologicalcharacteristics.

In some implementations, the present disclosure relates to a method ofmanaging power in a wearable computing device. The method comprisesdirecting light from a light source into tissue of a user during a firsttime period, generating a first light detector signal using askin-facing light detector, the first light detector signal indicating afirst amount of light detected by the light detector during the firstperiod, deactivating the light source during a second period, generatinga second light detector signal using the skin-facing light detector, thesecond light detector signal indicating a second amount of lightdetected by the light detector during the second period, generating aphysiological metric signal based at least in part on the first lightdetector signal and the second light detector signal, and modifying abrightness level of an electronic display based at least in part on thesecond light detector signal.

Generating the physiological metric signal may comprise generating anambient light cancellation signal based on the second light detectorsignal and cancelling ambient light in the first light detector signalusing the ambient light cancellation signal. In certain embodiments,generating the ambient light cancellation signal further comprisesconditioning the second light detector signal to account for skin tonecharacteristics of the user. The method may further comprise at leastpartially reversing the conditioning of the second light detector signalto produce a raw ambient light signal, wherein said modifying thebrightness level of the electronic display is based at least in part onthe raw ambient light signal. In certain embodiments, the method furthercomprises determining whether an amplitude of the raw ambient lightsignal is greater than a threshold.

In certain embodiments, the method further comprises determining anamount of sun exposure of the user based at least in part on the secondlight detector signal. In certain embodiments, the method may furthercomprise storing a value associated with the second light detectorsignal in a circular buffer. In certain embodiments, the method furthercomprises determining whether an amplitude of the second light detectorsignal is greater than a threshold. In certain embodiments, modifyingthe brightness level of the electronic display comprises adjusting thebrightness level from a first state to a second state. For example, thefirst state may correspond to a low-light mode and the second state maycorrespond to a high-light mode.

The method may further include determining one or more physiologicalcharacteristics of the user, adjusting one or more illuminationparameters of the light source based on the determined one or morephysiological characteristics and adjusting one or more receptionparameters of the light detector based on the determined one or morephysiological characteristics.

In some implementations, the present disclosure relates to a biometricmonitoring device comprising a physiological metric monitor moduleincluding a light source and a light detector associated with a backside of the biometric monitoring device, the physiological metricmonitor module being configured to generate a physiological metricsignal when the light source is turned on, and control circuitryconfigured to determine an amount of ambient light present using thelight detector associated with the back side of the biometric monitoringdevice when the light source is turned off.

In certain embodiments, the biometric monitoring device furthercomprises an electronic display associated with a front side of thebiometric monitoring device, wherein the control circuitry is furtherconfigured to adjust a brightness level setting of the electronicdisplay based at least in part on the determined amount of ambientlight. The physiological metric monitor module may be further configuredto generate the physiological metric signal when the light source isturned off.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments are depicted in the accompanying drawings forillustrative purposes, and should in no way be interpreted as limitingthe scope of the inventions. In addition, various features of differentdisclosed embodiments can be combined to form additional embodiments,which are part of this disclosure. Throughout the drawings, referencenumbers may be reused to indicate correspondence between referenceelements.

FIG. 1 is a block diagram illustrating an embodiment of a biometricmonitoring device according to one or more embodiments.

FIG. 2 provides a perspective front and side view of a wearablebiometric monitoring device according to one or more embodiments.

FIG. 3 provides a perspective back and side view of the wearablebiometric monitoring device of FIG. 2 according to one or moreembodiments.

FIG. 4 provides a cross-sectional view of the biometric monitoringdevice of FIG. 2 according to one or more embodiments.

FIG. 5 provides a cross sectional view of a sensor protrusion of abiometric monitoring device according to one or more embodiments.

FIG. 6 provides a cross sectional view of a sensor protrusion of abiometric monitoring device according to one or more embodiments.

FIG. 7A illustrates photoplethysmograph (PPG) sensor module according toone or more embodiments.

FIGS. 7B and 7C illustrate examples of a PPG sensor having aphotodetector and two LED light sources according to one or moreembodiments.

FIG. 8 illustrates an example of an optimized PPG detector according toone or more embodiments.

FIG. 9 provides a perspective front and side view of a wearablebiometric monitoring device according to one or more embodiments.

FIG. 10 provides a perspective back and side view of a wearablebiometric monitoring device according to one or more embodiments.

FIG. 11A illustrates an example block diagram of a PPG sensor which hasa light source, light detector, ADC, processor, DAC/GPIOs, and lightsource intensity and on/off control according to one or moreembodiments.

FIG. 11B illustrates an example block diagram of a PPG sensor that issimilar to that of FIG. 11A which additionally uses a sample-and-holdcircuit as well as analog signal conditioning according to one or moreembodiments.

FIG. 11C illustrates an example block diagram of a PPG sensor that issimilar to that of FIG. 11A which additionally uses a sample-and-holdcircuit according to one or more embodiments.

FIG. 11D illustrates an example block diagram of a PPG sensor havingmultiple switchable light sources and detectors, light sourceintensity/on and off control, and signal conditioning circuitryaccording to one or more embodiments.

FIG. 11E illustrates an example block diagram of a PPG sensor which usessynchronous detection. To perform this type of PPG detection, it has ademodulator according to one or more embodiments.

FIG. 11F illustrates an example block diagram of a PPG sensor which, inaddition to the features of the sensor illustrated in FIG. 11A, has adifferential amplifier according to one or more embodiments.

FIG. 11G illustrates an example block diagram of a PPG sensor accordingto one or more embodiments.

FIG. 12A illustrates an example schematic of a sample-and-hold circuitand differential/instrumentation amplifier which may be used in PPGsensing according to one or more embodiments.

FIG. 12B illustrates an example schematic of a circuit for a PPG sensorusing a controlled current source to offset “bias” current prior to atransimpedance amplifier according to one or more embodiments.

FIG. 12C illustrates an example schematic of a circuit fora PPG sensorusing a sample-and-hold circuit for current feedback applied tophotodiode according to one or more embodiments.

FIG. 12D illustrates an example schematic of a circuit fora PPG sensorusing a differential/instrumentation amplifier with ambient lightcancellation functionality according to one or more embodiments.

FIG. 12E illustrates an example schematic of a circuit for a PPG sensorusing a photodiode offset current generated dynamically by a DACaccording to one or more embodiments.

FIG. 12F illustrates an example schematic of a circuit for a PPG sensorusing a photodiode offset current generated dynamically by a controlledvoltage source according to one or more embodiments.

FIG. 12G illustrates an example schematic of a circuit for a PPG sensorincluding ambient light removal functionality using a “switchedcapacitor” method according to one or more embodiments.

FIG. 12H illustrates an example schematic of a circuit fora PPG sensorthat uses a photodiode offset current generated by a constant currentsource according to one or more embodiments.

FIG. 12I illustrates an example schematic of a circuit for a PPG sensorthat includes ambient light removal functionality and differencingbetween consecutive samples according to one or more embodiments.

FIG. 12J illustrates an example schematic of a circuit for ambient lightremoval and differencing between consecutive samples according to one ormore embodiments.

FIG. 13 shows an example light emission driver circuit for driving alight emitter to emit a light signal onto a region of the skin of a useraccording to one or more embodiments.

FIG. 14 shows a block diagram of an example light detection circuit fordetecting a scattered light signal and for outputting an output signalbased on the scattered light signal according to one or moreembodiments.

FIG. 15 shows an example circuit for implementing the light detectioncircuit of FIG. 14 according to one or more embodiments.

FIG. 16 is a flow diagram illustrating a process for adjusting abacklighting setting of an electronic display according to one or moreembodiments.

FIG. 17 is a block diagram illustrating an embodiment of a displaycontrol feedback system according to one or more embodiments.

DETAILED DESCRIPTION

The headings provided herein are for convenience only and do notnecessarily affect the scope or meaning of the claimed invention. Likereference numbers and designations in the various drawings may or maynot indicate like elements.

Although certain preferred embodiments and examples are disclosed below,inventive subject matter extends beyond the specifically disclosedembodiments to other alternative embodiments and/or uses and tomodifications and equivalents thereof. Thus, the scope of the claimsthat may arise herefrom is not limited by any of the particularembodiments described below. For example, in any method or processdisclosed herein, the acts or operations of the method or process may beperformed in any suitable sequence and are not necessarily limited toany particular disclosed sequence. Various operations may be describedas multiple discrete operations in turn, in a manner that may be helpfulin understanding certain embodiments; however, the order of descriptionshould not be construed to imply that these operations are orderdependent. Additionally, the structures, systems, and/or devicesdescribed herein may be embodied as integrated components or as separatecomponents. For purposes of comparing various embodiments, certainaspects and advantages of these embodiments are described. Notnecessarily all such aspects or advantages are achieved by anyparticular embodiment. Thus, for example, various embodiments may becarried out in a manner that achieves or optimizes one advantage orgroup of advantages as taught herein without necessarily achieving otheraspects or advantages as may also be taught or suggested herein.

Overview

Biometric monitoring devices, including wrist-worn biometric monitoringdevices, can include display screens powered by an internal powersource. Due to power and/or visibility considerations, it may bedesirable for the brightness setting of the display screen to beadjusted from time to time. For example, when ambient light levels arehigh, it may be desirable for the brightness setting of the display tobe at a high level, while when ambient light levels are low, it may bedesirable for the brightness setting of the display to be at a lowerlevel in order to save power and/or reduce the visual strain on the useror reduce other effects associated with over-lighting.

In order to make backlight setting adjustment based on ambient lighting,it may be necessary to generate or otherwise determine informationindicating the ambient light level. Brightness level settings forelectronic displays, as described herein in connection with variousembodiments, may be implemented in any suitable or desirable manner. Forexample, with respect to liquid crystal display (LCD) devices, thebrightness level of the display may be controlled using one or morebacklighting devices and/or subsystems. Backlighting devices/subsystemsmay generally direct light to the electronic display from behind thedisplay. In certain devices, display brightness may be achieved at leastin part by reflecting environmental ambient light to light the displayas an alternative to, or in addition to, providing light from abacklight device/subsystem. For example, certain devices may include anat least partially transparent light guide structure configured toreflect light entering the light guide from side or edge portionsthereof towards the display screen. Although certain embodimentsdisclosed herein may be described in the context of backlighting devicesand/or subsystems, it should be understood that display brightness levelsetting adjustment in accordance with the present disclosure mayimplement any suitable or desirable lighting mechanism, and thatdescription herein of backlighting brightness level adjustment should beunderstood to relate to brightness level setting adjustment fornon-backlighting devices/subsystems as well.

Ambient light determinations may be made using dedicated ambient lightsensors, such as in the form of an outward-facing sensor disposed on orbelow the display screen of a biometric monitoring device. Dedicatedambient light sensors may provide relatively high fidelity dataindicating ambient lighting conditions. Biometric monitoring devicesthat do not include ambient light sensing functionality may lack theability to adjust display brightness settings based on ambient lightingconditions, and therefore may necessarily maintain the displaybrightness at a maximum operational level at all times to account forthe brightest expected ambient light conditions, such as direct outdoorsunlight conditions. The inability to intelligently modify thebrightness level setting of the display can have an adverse effect on abiometric monitoring device's battery life, among other things.Therefore, dedicated ambient light sensors may be used to adjust thebrightness of a display to conserve battery power and/or provide animproved user experience.

Certain embodiments disclosed herein provide for display brightnesslevel setting adjustment, such as backlighting adjustment, without theaid of an outward-facing dedicated ambient light sensor. For example,biometric monitoring devices in accordance with the present disclosuremay incorporate one or more existing functional components or modulesdesigned for determining one or more physiological metrics associatedwith a user (e.g., wearer) of the device, such as a heart rate sensor orthe like. Such components/modules may be disposed or associated with anunderside/backside of the biometric monitoring device, and may generallynot be in direct exposure to a substantial portion of the ambient lightthat is present when the biometric monitoring device is worn by a user.For example, where the biometric monitoring device is worn on the user'swrist, the physiological metric component(s)/module(s) may be associatedwith an underside/backside of the device substantially opposite thedisplay and facing the arm of the user. However, certainunderside/backside physiological metric sensor devices or subsystems,such as heart rate sensors in accordance with the present disclosure,may nevertheless be configurable to provide signals indicative ofambient lighting conditions through indirect, or reflective, lightdetection.

Certain embodiments disclosed herein provide for biometric monitoringdevices that utilize ambient light readings derivable from aphysiological metric sensor, such as a hear rate sensor (e.g.,photoplethysmograph sensor) associated with an underside of a wrist-worndevice, for adjusting brightness level settings for the device'selectronic display. For example, ambient light readings from a backsidephysiological metric sensor may be converted to a common reference framefor utilization thereof. Ambient light determination using a backsidephysiological metric sensor may provide relatively more basic ambientlight information than may be achievable using a dedicatedoutward-facing ambient light sensor, but may still provide adequateinformation from which to make ambient light determinations among afinite set of ambient light level ranges, such as determining whetherambient lighting conditions indicate indoor or outdoor lighting.Therefore, certain embodiments disclosed herein allow for the detectionof indoor versus outdoor lighting conditions without a dedicatedoutward-facing ambient light sensor by leveraging an existingphysiological metric sensor, thereby providing savings with respect topower and extended battery life.

Biometric Monitoring

In some implementations, the present disclosure is related to biometricmonitoring devices. The term “biometric monitoring device” is usedherein according to its broad and ordinary meaning, and may be used invarious contexts herein to refer to any type of biometric trackingdevices, personal health monitoring devices, portable monitoringdevices, portable biometric monitoring devices, or the like. In someembodiments, biometric monitoring devices in accordance with the presentdisclosure may be wearable devices, such as may be designed to be worn(e.g., continuously) by a person (i.e., “user,” “wearer,” etc.). Whenworn, such biometric monitoring devices may be configured to gather dataregarding activities performed by the wearer, or regarding the wearer'sphysiological state. Such data may include data representative of theambient environment around the wearer or the wearer's interaction withthe environment. For example, the data may comprise motion dataregarding the wearer's movements, ambient light, ambient noise, airquality, etc., and/or physiological data obtained by measuring variousphysiological characteristics of the wearer, such as heart rate,perspiration levels, and the like.

In some cases, a biometric monitoring device may leverage other devicesexternal to the biometric monitoring device, such as an external heartrate monitor in the form of an EKG sensor for obtaining heart rate data,or a GPS receiver in a smartphone may be used to obtain position data,for example. In such cases, the biometric monitoring device maycommunicate with these external devices using wired or wirelesscommunications connections. The concepts disclosed and discussed hereinmay be applied to both stand-alone biometric monitoring devices as wellas biometric monitoring devices that leverage sensors or functionalityprovided in external devices, e.g., external sensors, sensors orfunctionality provided by smartphones, etc.

Biometric Monitoring Devices

Systems, devices and/or methods/processes in accordance with the presentdisclosure may comprise, or be implemented in connection with, abiometric monitoring device Embodiments of the present disclosure mayprovide biometric monitoring devices configured to adjust electronicdisplay brightness level settings using ambient light informationderived from one or more physiological metric sensors associated with anunderside/backside of the biometric monitoring device. It is to beunderstood that while the concepts and discussion included herein arepresented in the context of biometric monitoring devices, these conceptsmay also be applied in other contexts as well if the appropriatehardware is available. For example, some or all of the relevant sensorfunctionality may be incorporated in one or more external computingdevices (e.g., smartphone) communicatively coupled to the biometricmonitoring device.

FIG. 1 is a block diagram illustrating an embodiment of a biometricmonitoring device 100 in accordance with one or more embodimentsdisclosed herein. The biometric monitoring device 100 may be worn by auser 10. The biometric monitoring device 100 may include one or moreelectronic display units or modules 130, such as a touchscreen display,or the like. In certain embodiments, the electronic display 130 may beassociated with the front side of the biometric monitoring device 100.For example, in wearable embodiments of the biometric monitoring device100, the electronic display 130 may be configured to be externallypresented to a user viewing the biometric monitoring device 100. Incertain embodiments, the electronic display is illuminated usingbacklighting, or other lighting mechanism, according to a brightnesslevel setting. In certain embodiments, the display 130 is a front-facingorganic light emitting diode (OLED) display. Driving the illumination ofthe electronic display 130 may represent one of the largest powerconsumers of the biometric monitoring device 100. In certainembodiments, the brightness of the electronic display is modifiedaccording to an ambient light determination, which may, in some cases,provide a power savings of approximately 20-30%, or more, with respectto battery life of the device by reducing the power applied toilluminate the display 130 during certain periods.

Front-facing ambient light sensors may have additionalhardware/circuitry associated therewith. Furthermore, it may bedesirable to provide display screen treatment to accommodatefront-facing ambient light sensors, such as a window in the displayscreen where the display screen is at least partially covered underneathwith a dark paint or the like. While certain front-facing displays ofbiometric monitoring devices may have dedicated ambient light sensorsassociated therewith, the biometric monitoring device 100 may beconfigured to make ambient light determinations without a dedicatedambient light sensor, and may instead repurpose ambient-light-relateddata from a separate back-facing physiological metric sensor 141 (e.g.,optical sensor). By leveraging ambient light data generated using aback-facing physiological metric sensor, certain embodiments disclosedhere may advantageously provide cost savings and/or reduced devicecomplexity

The biometric monitoring device 100 includes control circuitry 110.Although certain modules and/or components are illustrated as part ofthe control circuitry 110 in the diagram of FIG. 1 , it should beunderstood that control circuitry associated with the biometricmonitoring device 100 and/or other components or devices in accordancewith the present disclosure may include additional components and/orcircuitry, such as one or more of the additional illustrated componentsof FIG. 1 . Furthermore, in certain embodiments, one or more of theillustrated components of the control circuitry 110 may be omittedand/or different than that shown in FIG. 1 and described in associationtherewith. The term “control circuitry” is used herein according to itsbroad and ordinary meaning, and may include any combination of softwareand/or hardware elements, devices or features, which may be implementedin connection with operation of the biometric monitoring device 100.Furthermore, the term “control circuitry” may be used substantiallyinterchangeably in certain contexts herein with one or more of the terms“controller,” “integrated circuit,” “IC,” “application-specificintegrated circuit,” “ASIC,” “controller chip,” or the like.

The control circuitry 110 may comprise one or more processors, datastorage devices, and/or electrical connections. For example, the controlcircuitry 110 may comprise one or more processors configured to executeoperational code for the biometric monitoring device 100, such asfirmware or the like, wherein such code may be stored in one or moredata storage devices of the biometric monitoring device 100. In oneembodiment, the control circuitry 110 is implemented on an SoC (systemon a chip), though those skilled in the art will recognize that otherhardware/firmware implementations are possible.

The control circuitry 110 may comprise a brightness level managementmodule 111. The brightness level management module 111 may comprise oneor more hardware and/or software components or features configured tocontrol a brightness level setting for the electronic display 130. Incertain embodiments, the brightness level management module 111 maycomprise ambient light detection functionality, wherein data associatedwith, or indicative of, ambient lighting conditions of an environment inwhich the biometric monitoring device 100 is disposed may be used todetermine an appropriate or desirable brightness level setting for theelectronic display 130.

The control circuitry 110 may further comprise an optical physiologicalmetric sensor 141 that includes: a physiological metric calculationmodule 115, which may be configured to determine one or morephysiological metrics associated with the user 10 of the biometricmonitoring device 100; light source(s) 140 located on the backside ofthe device, which may be configured to emit light in one or morewavelengths; and light detector(s) 145 located on the backside of thedevice, which may be configured to detect light reflected from thetissue of the user 10. As is discussed below, the optical physiologicalmetric sensor 141 may include circuitry configured to detect ambientlighting conditions using the light detector(s) 145 in order to subtractor cancel the unwanted ambient light from the optical readings of thelight detector(s) 145. For example, ambient light reflected into thelight detector(s) 145 may distort the sensor signal that is designed togenerate readings indicative of light originating from the lightsources(s) 140.

The physiological metric calculation module 115 may be configured togenerate physiological metric data based on readings from one or morelight detectors 145, and/or one or more other sensor devices 155. Thelight detectors 145 may be configured to detect light generated by oneor more light sources 140, as well as ambient light to which thedetector 145 is exposed.

As mentioned above, the light sources 140 and/or light detector 145 maybe associated with the backside of the biometric monitoring device 100.For example, in a wearable configuration of the biometric monitoringdevice 100, whereas the electronic display may be generallyoutward-facing, the light sources 140 and/or light detectors 145 may bephysically connected to and/or associated with an underside (i.e.,backside) of the biometric monitoring device that may be generallyskin-facing when worn by the user 10, such as on a wrist, arm, leg, orother appendage or body part of the user 10.

In operation, in certain embodiments, the physiological metriccalculation module 115 may be configured to activate the light source(s)140 and/or otherwise cause the light source(s) 140 to generate or directthe light in a direction towards the tissue or body of the user 10,wherein the light detector(s) 145 detects light reflecting back from theuser. Such detected reflected light from the user may be used todetermine one or more physiological metrics associated with the user 10,such as heart rate, blood oxygenation, or the like. To the extent thatthe reflected light detected by the light detector 145 includes director reflected ambient light in addition to the light generated by thelight source(s) 140, such additional light may undesirably obfuscate thedetermination of the relevant physiological metric(s). Therefore, incertain embodiments, the physiological metric calculation module 115 maybe configured to at least partially cancel out the detected ambientlight in order to provide more accurate physiological metriccalculation. In certain embodiments, the physiological metriccalculation module 115 may cancel out the ambient light at least in partby utilizing a reading from the light detector 145 during a period oftime in which the light sources 140 are not activated in order to obtaina reading indicative of the ambient light exposed to the light detector145. In order to promote correspondence between the ambient lightdetected during the period in which the light sources 140 are not activeand the period in which the light sources 140 are active, such periodsmay advantageously be temporally close to one another.

The biometric monitoring device may further comprise one or more datastorage modules 151, which may include any suitable or desirable type ofdata storage, such as solid-state memory, which may be volatile ornon-volatile. In some embodiments the memory is non-transitory.Solid-state memory of the biometric monitoring device 100 may compriseany of a wide variety of technologies, such as flash integratedcircuits, Phase Change Memory (PC-RAM or PRAM), ProgrammableMetallization Cell RAM (PMC-RAM or PMCm), Ovonic Unified Memory (OUM),Resistance RAM (RRAM), NAND memory, NOR memory, EEPROM, FerroelectricMemory (FeRAM), MRAM, or other discrete NVM (non-volatile solid-statememory) chips. The data storage 151 may be used to store system data,such as operating system data and/or system configurations orparameters. The biometric monitoring device 100 may further comprisedata storage utilized as a buffer and/or cache memory for operationaluse by the control circuitry 110.

The biometric monitoring device 100 further comprises power storage 153,which may comprise a rechargeable battery, one or more capacitors, orother charge-holding device(s). The power stored by the power storagemodule 153 may be utilized by the control circuitry 110 for operation ofthe biometric monitoring device 100, such as for powering the lightsources 140 and/or display 130. The power storage module 153 may receivepower over the host interface 176 or through other means.

The biometric monitoring device 100 may further comprise one or moreconnectivity components 170, which may include, for example, a wirelesstransceiver 172. The wireless transceiver 172 may be communicativelycoupled to one or more antenna devices 195, which may be configured towirelessly transmit/receive data and/or power signals to/from thebiometric monitoring device. For example, the wireless transceiver 172may be utilized to communicate data and/or power between the biometricmonitoring device 100 and an external host system (not shown), which maybe configured to interface with the biometric monitoring device 100. Incertain embodiments, the biometric monitoring device 100 may compriseadditional host interface circuitry and/or components 176, such as wiredinterface components for communicatively coupling with a host device orsystem to receive data and/or power therefrom and/or transmit datathereto.

The connectivity circuitry 170 may further comprise user interfacecomponents 174 for receiving user input. For example, the user interface174 may be associated with the electronic display 130, wherein theelectronic display is a touchscreen display configured to receive userinput from user contact therewith. The user interface module 174 mayfurther comprise one or more buttons or other input components orfeatures.

The connectivity circuitry 170 may further comprise the host interface176, which may be, for example, an interface for communicating with ahost device or system (not shown) over a wired or wireless connection.The host interface 176 may be associated with any suitable or desirablecommunication protocol and/or physical connector, such as UniversalSerial Bus (USB), Micro-USB, WiFi, Bluetooth, FireWire, PCIe, or thelike. For wireless connections, the host interface 176 may beincorporated with the wireless transceiver 172.

The biometric monitoring device 100 may be configured to implementintelligent brightness level setting adjustment for the electronicdisplay based on data generated by the physiological metric sensor 141.Although certain functional modules and components are illustrated anddescribed herein, it should be understood that ambient light sensingand/or brightness level setting adjustment functionality in accordancewith the present disclosure may be implemented using a number ofdifferent approaches. For example, in some implementations the controlcircuitry 110 may comprise one or more processors controlled bycomputer-executable instructions stored in non-transitory memory (e.g.,a non-transitory storage medium) so as to provide functionality such asis described herein. In other implementations, such functionality may beprovided in the form of one or more specially-designed electricalcircuits. In some implementations, such functionality may be provided byone or more processors controlled by computer-executable instructionsstored in a memory coupled with one or more specially-designedelectrical circuits. Various examples of hardware that may be used toimplement the concepts outlined herein include, but are not limited to,application specific integrated circuits (ASICs), field-programmablegate arrays (FPGAs), and general-purpose microprocessors coupled withmemory that stores executable instructions for controlling thegeneral-purpose microprocessors.

Standalone biometric monitoring devices may be implemented in a numberof form factors and may be designed to be worn in a variety of ways. Insome implementations, a biometric monitoring device may be designed tobe insertable into a wearable case or into one or more of multipledifferent wearable cases (e.g., a wristband case, a belt-clip case, apendant case, a case configured to be attached to a piece of exerciseequipment such as a bicycle, etc.). Certain such implementations aredescribed in more detail in, for example, U.S. Pub. No. 2014/0180019,published on Jun. 26, 2014, which is hereby incorporated by referencefor such purpose. In other implementations, a biometric monitoringdevice may be designed to be worn in limited manners, such as abiometric monitoring device that is integrated into a wristband in anon-removable manner and may be intended to be worn specifically on aperson's wrist (or perhaps ankle).

Wearable biometric monitoring devices according to embodiments andimplementations described herein may have shapes and sizes adapted forcoupling to (e.g., secured to, worn, borne by, etc.) the body orclothing of a user. An example of a wearable biometric monitoring device201 is shown in FIG. 2 . FIG. 2 shows perspective front and side viewsof the wearable biometric monitoring device 201. The wearable biometricmonitoring device 201 includes both a biometric monitoring device 200,as well as a band portion 207. In certain embodiments, the band portion207 includes first and second portions that may be connected by a claspportion 209. The biometric monitoring device portion 200 may beinsertable, and may have any suitable or desirable dimensions. Wearablebiometric monitoring devices may generally be relatively small in sizeso as to be unobtrusive for the wearer. The biometric monitoring device200 may be designed to be able to be worn without discomfort for longperiods of time and to not interfere with normal daily activity.

The electronic display 230 may comprise any type of electronic displayknown in the art. For example, the display 230 may be a liquid crystaldisplay (LCD) or organic light emitting diode (OLED) display, such as atransmissive LCD or OLED display. The electronic display 230 may beconfigured to provide brightness, contrast, and/or color saturationfeatures according to display settings maintained by control circuitryand/or other internal components/circuitry of the biometric monitoringdevice 200. The brightness of the display 230 may be implemented throughthe use of a brightness component. In certain embodiments, thebrightness component can include backlighting mechanisms, which maycomprise one or more internal light sources positioned behind thedisplay screen to provide illumination thereto. In some embodiments, thebacklighting component comprises one or more light-emitting diodes(LEDs) (e.g., white LEDs). The terms “backlight,” “backlighting,”“backlighting component,” “backlighting mechanism,” “backlightingsubsystem,” and “backlighting module” are used herein according to theirbroad and ordinary meanings, and may be used to refer generally to oneor more lighting devices that may be activated to illuminate a displayor otherwise make a display more visible to a user, and/or to circuitry(hardware and/or code) for managing or controlling a brightness settingof an electronic display. In some contexts, the above-recited terms maybe used to refer to an actual brightness, or quantity of light, producedor generated by an electronic display. In other contexts, theabove-recited terms may be used to refer to a separate lightingcomponent that produces or generates ambient light (reflective light orillumination), transmissive light, or some combination thereof(transflective light or illumination) with respect to the electronicdisplay. By adjusting the brightness of the electronic display 130, thebrightness level management module 111 may provide power savings.

The power consumption associated with the display illumination componentcan be relatively high in some embodiments, particularly whenimplementing a maximum brightness level. Although a maximum brightnesslevel setting may be desirable in outdoor daylight conditions, certainembodiments of the present disclosure advantageously provide forintelligent brightness level adjustment, which may provide power savingswhen the brightness level is set to a reduced brightness state, such aswhen the ambient light levels are below outdoor daylight levels. In someimplementations, such power savings may be achieved without the use ofdedicated ambient light sensors on, or associated with, theoutward-facing surface of an electronic display

FIG. 3 is a perspective back and side view of the wearable biometricmonitoring device 201 of FIG. 2 . The wearable biometric monitoringdevice 201 comprises a band portion 207, which may be configured to belatched or secured about a user's arm or other appendage via asecurement mechanism of any suitable or desirable type. For example, theband 207 may be secured using a hook and loop clasp component 209. Incertain embodiments, the band 207 is designed with shape memory topromote wrapping around the user's arm.

The wearable biometric monitoring device 201 includes a biometricmonitoring device component 200, which may be at least partially securedto the band 207. The view of FIG. 3 shows a backside 206 (also referredto herein as the “underside”) of the biometric monitoring device 200,which may generally face and/or contact skin or clothing associated withthe user's arm, for example. The terms “backside” and “underside” areused herein according to their broad and ordinary meaning, and may beused in certain contexts to refer to a side, panel, region, component,portion and/or surface of a biometric monitoring device that ispositioned and/or disposed substantially opposite to a user displayscreen, whether exposed externally of the device, or at least partiallyinternal to an electronics package or housing of the device.

The biometric monitoring device 200 may include one or more buttons 203,which may provide a mechanism for user input. The biometric monitoringdevice 200 may further comprise a device housing, which may comprise oneor more of steel, aluminum, plastic, and/or other rigid structure. Thehousing 208 may serve to protect the biometric monitoring device 200and/or internal electronics/components associated therewith fromphysical damage and/or debris. In certain embodiments, the housing 208is at least partially waterproof.

The backside 206 of the biometric monitoring device 200 may have anoptical physiological metric sensor 243 associated therewith, which maycomprise one or more sensor components, such as one or more lightsources 240 and/or light detectors 245, the collection of which mayrepresent an example of the optical physiological metric sensor 141 ofFIG. 1 . In certain embodiments, the optical physiological metric sensor243 comprises a protrusion form protruding from the back surface of thebiometric monitoring device 200. The sensor components may be used todetermine one or more physiological metrics of a user wearing thewearable biometric monitoring device 201. For example, the opticalphysiological sensor components associated with the sensor 243 may beconfigured to provide readings used to determine heart rate (e.g., inbeats-per-minute (BPM)), blood oxygenation (e.g., SpO₂), blood pressure,or other metric. In certain embodiments, the biometric monitoring device200 further includes an electrical charger mating recess 209.

As the sensor 243 may be present and configured to detect ambient lightin connection with heart-rate-related optical measurements, or othertype of physiological parameter measurement, certain embodimentsdisclosed herein may advantageously leverage or repurpose the ambientlight signal(s) associated with the sensor 243 for the purpose of makinga determination relating to ambient light conditions. For example,ambient light determinations may advantageously indicate whether thebiometric monitoring device 200 is indoors or outdoors.

Generally, lighting conditions outdoors may be substantially greaterwith respect to luminous flux than lighting conditions indoors. When thesensor 243 is used to take optical readings of light that is reflectedback into the sensor from the user's tissue/blood, such readings maygenerally comprise a combination of ambient light and reflected lightfrom the light sources 240. Therefore, in order to obtain a reading thatis not influenced by the ambient light, it may be desirable to cancelthe ambient light from the sensor signal(s)/data. In order to achievesuch cancellation, the sensor 243 may implement a phase during which thelight sensor(s) 245 is/are read without the light source(s) beingactive, such that detected light is substantially wholly attributable toambient light. The light source(s) 140 may then be activated, whereinthe resulting light detection is processed in such a way as to at leastpartially subtract the ambient light read during the off phase, therebyproviding a signal/data that is estimated to be attributablesubstantially wholly to the light generated by the device 200. Incertain embodiments, the ambient light readings used to cancel ambientlight may be obtained during a phase in which the light source(s) areactively emitting light. For example, in one implementation, the sensor243 may be configured to detect ambient light in a first phase in whichthe light emitter(s) of the sensor 243 are turned off, and again in asecond phase in which the light emitter(s) are turned on. For example,in the second phase, the light emitter(s) may be driven at a relativelylow level. Additional embodiments and details relating to ambient lightdetection are disclosed in U.S. patent application Ser. No. 15/223,589,entitled “Circuits and Methods for Photoplethysmographic Sensor,” filedon Jul. 29, 2016, the disclosure of which is hereby explicitlyincorporated by reference in its entirety.

Because the light detector 245 is disposed on the backside of the device200, which is generally at least partially shielded from direct lightwhen worn by the user, the ambient light reading from the light detector245 may not be as precise as certain other ambient light sensorembodiments. However, when making a simple binary determination ofwhether the device is indoors or outdoors, the relatively crude ambientlight information may nevertheless be sufficient. Therefore, it may notbe necessary to implement a forward-facing ambient light sensor; rather,relatively basic assessment of ambient light conditions may be adequate,and dynamic adjustment of display brightness level may be unnecessary.When it is determined that the biometric monitoring device 200 isoutdoors, the device may implement a full brightness setting or mode,whereas a less bright setting or mode may be used where indoor lightingis detected.

Although the sensor 243 is illustrated as comprising a protrusion formcertain figures herein, it should be understood that backside sensormodules in accordance with the present disclosure may or may not beassociated with a protrusion form. In certain embodiments, theprotrusion form on the backside of the device may be designed to engagethe skin of the user with more force than the surrounding device body.In certain embodiments, an optical window or light-transmissivestructure may be incorporated in a portion of the protrusion 243. Thelight emitter(s) 240 and/or detector(s) 245 of the sensor module 243 maybe disposed or arranged in the protrusion 243 near the window orlight-transmissive structure. As such, when attached to the user's body,the window portion of the protrusion 243 of the biometric monitoringdevice 200 may engage the user's skin with more force than thesurrounding device body, thereby providing a more secure physicalcoupling between the user's skin and the optical window. That is, theprotrusion 243 may cause sustained contact between the biometricmonitoring device and the user's skin that may reduce the amount ofstray light measured by the photodetector 245, decrease relative motionbetween the biometric monitoring device 200 and the user, and/or provideimproved local pressure to the user's skin, some or all of which mayincrease the quality of the cardiac signal of interest generated by thesensor module. Notably, the protrusion 243 may contain other sensorsthat benefit from close proximity and/or secure contact to the user'sskin. These may be included in addition to or in lieu of a heart ratesensor and may include sensors such as a skin temperature sensor (e.g.,noncontact thermopile that utilizes the optical window or thermistorjoined with thermal epoxy to the outer surface of the protrusion), pulseoximeter, blood pressure sensor, EMG, or galvanic skin response (GSR)sensor.

In certain embodiments, a portion of the backside of the biometricmonitoring device 200 may include a friction-enhancing mechanism ormaterial. For example, the backside of the biometric monitoring device200 may include a plurality of raised or depressed regions or portions(for example, small bumps, ridges, grooves, and/or divots). Moreover, afriction enhancing material (for example, a gel-like material such assilicone or other elastomeric material) may be disposed on theskin-side, while may further improve user comfort and/or prevent straylight from entering. The use of a protrusion and/or friction may improvemeasurement accuracy of data acquisition corresponding to certainparameters (e.g., heart rate, heart rate variability, galvanic skinresponse, skin temperature, skin coloration, heat flux, blood pressure,blood glucose, etc.) by reducing motion of the biometric monitoringdevice 200 (and thus of the sensor) relative to the user's skin duringoperation, particularly while the user is in motion.

Some or all of the backside housing 208 of the biometric monitoringdevice 200 may comprise a metal material (for example, steel, stainlesssteel, aluminum, magnesium, or titanium). Such a configuration mayprovide desirable structural rigidity. In certain embodiments, thehousing 208 is at least partially ferrous (for example, a grade ofstainless steel that is ferrous). In such embodiments, the biometricmonitoring device 200 may interconnect with a charger via a connectorthat secures itself to the biometric monitoring device using magnetsthat couple to the ferrous material. The biometric monitoring device 200may also engage a dock or docking station, using such magneticproperties, to facilitate data and/or power transfer. Moreover, such ahousing may provide enhanced electromagnetic shielding that may enhancethe integrity and/or reliability of the optical physiological sensor(e.g., heart rate sensor) and the physiological metric data acquisitionprocess/operation.

The biometric monitoring device 200 may be configured to collect one ormore types of physiological and/or environmental data from embeddedsensors and/or external devices and communicate or relay suchinformation to other devices, including devices capable of serving as anInternet-accessible data sources, thus permitting the collected data tobe viewed, for example, using a web browser or network-basedapplication. For example, while the user is wearing the biometricmonitoring device 200, the biometric monitoring device 200 may calculateand store the user's step count using one or more biometric sensors. Thebiometric monitoring device may then transmit data representative of theuser's step count to an account on a web service, computer, mobilephone, or health station where the data may be stored, processed, andvisualized by the user. Indeed, the biometric monitoring device 200 maymeasure or calculate a plurality of other physiological metrics inaddition to, or in place of, the user's step count. These include, butare not limited to, energy expenditure, e.g., calorie burn, floorsclimbed and/or descended, heart rate, heart rate variability, heart raterecovery, location and/or heading, e.g., through GPS or a similarsystem, elevation, ambulatory speed and/or distance traveled, swimminglap count, swimming stroke type and count detected, bicycle distanceand/or speed, blood pressure, blood glucose, skin conduction, skinand/or body temperature, muscle state measured via electromyography,brain activity as measured by electroencephalography, weight, body fat,caloric intake, nutritional intake from food, medication intake, sleepperiods, e.g., clock time, sleep phases, sleep quality and/or duration,pH levels, hydration levels, respiration rate, and other physiologicalmetrics.

The biometric monitoring device 200 may also measure or calculatemetrics related to the environment around the user such as barometricpressure, weather conditions (e.g., temperature, humidity, pollen count,air quality, rain/snow conditions, wind speed), light exposure (e.g.,ambient light, UV light exposure, time and/or duration spent indarkness), noise exposure, radiation exposure, and magnetic field.Furthermore, the biometric monitoring device 200 or the system collatingthe data streams from the biometric monitoring device may calculatemetrics derived from such data. For example, the device or system maycalculate the user's stress and/or relaxation levels through acombination of heart rate variability, skin conduction, noise pollution,and sleep quality. In another example, the biometric monitoring device200 may determine the efficacy of a medical intervention, e.g.,medication, through the combination of medication intake, sleep data,and/or activity data. In yet another example, the biometric monitoringdevice or system may determine the efficacy of an allergy medicationthrough the combination of pollen data, medication intake, sleep and/oractivity data. These examples are provided for illustration only and arenot intended to be limiting or exhaustive. Further embodiments andimplementations of sensor devices may be found in U.S. Pat. No.9,167,991, titled “Portable Biometric Monitoring Devices and Methods ofOperating Same” filed Jun. 8, 2011, which is hereby incorporated hereinby reference in its entirety.

Physiological Metric Sensor Module

An optical physiological metric sensor such as photoplethysmography(PPG) sensors may generally utilize light sensors and/or detectors toobtain a volumetric measurement relating to pulsatile blood flow in thebody. PPG information may be obtained illuminating the skin of a subjectand measuring changes in light absorption. A PPG sensor can be designedto monitor the perfusion of blood to the dermis and/or subcutaneoustissue of the skin. PPG data may be determined using a wrist-wornbiometric monitoring device based on the pumping of blood to theperiphery during each cardiac cycle. While the pressure pulse may besomewhat damped by the time it reaches the skin, it may nevertheless beenough to distend the arteries and/or arterioles in the subcutaneoustissue of the wearer of the biometric monitoring device. The change involume caused by the pressure pulse may be detected by illuminating theskin with the light from one or more light source (e.g., light-emittingdiodes (LEDs)) and then measuring the amount of light either transmittedor reflected to one or more light sensors (e.g., photodiode(s)). Incertain embodiments, as blood flow to the skin can be modulated byvarious other physiological systems, the PPG sensor may further be usedto monitor breathing, hypovolemia, and/or other circulatory conditions.

PPG readings can be used to determine heart rate, SpO2, and the like.While PPGs can be obtained in certain systems using transmissiveabsorption, with respect certain wrist-worn biometric monitoring devicesdisclosed herein, PPG information may be obtained using reflectiveabsorption. For PPG signals, the DC component of the signal may beattributable to the bulk absorption of the skin tissue, while the ACcomponent may be attributable to variation in blood volume in the skincaused by the pressure pulse of the cardiac cycle. Generally, the heightof the AC component of the PPG signal may be proportional to the pulsepressure, which is the difference between the systolic and diastolicpressure in the arteries. Although certain embodiments are presentedherein in the context of PPG sensors, it should be understood thatambient light data for electronic display brightness level management inaccordance with the present disclosure may incorporate ambient lightsignals from any suitable or desirable physiological metric sensor.

FIG. 4 shows a cross-sectional view of the biometric monitoring device200 of FIGS. 2 and 3 according to one or more embodiments, which isattached to a band portion 207. The diagram of FIG. 4 shows across-section of the sensor protrusion 243 shown in FIG. 3 , exampleembodiments of which are illustrated in further detail in FIGS. 5 and 6and described below. Certain electronic/circuitry components of thebiometric monitoring device 200 may be mounted to or otherwiseassociated with a controller board 219, which may comprise, for example,one or more printed circuit boards (PCBs). The controller board 219 maycomprise controller circuitry operating the biometric monitoring device200. In certain embodiments, the sensor module 243 may be configured togenerate sensor signals and provide such sensor signals to thecontroller board circuitry for processing thereof. For example, thecontroller circuitry 110 of FIG. 1 and described above may beimplemented at least in part as a controller board like that shown inFIG. 4 .

The sensor protrusion 243 and/or associated components may be part of abackside, or underside, 206 of the biometric monitoring device 200. Thebackside 206 of the biometric monitoring device 200 may be positionedsubstantially opposite a front side 202, which may be associated with anelectronic display 230, which may be illuminated using backlighting orother lighting mechanism according to a brightness level setting managedat least in part by the controller board 219 as described herein.

In some implementations, the sensor protrusion 243 may comprise anoptical sensor, which may be positioned on the backside 206 (e.g.,skin-side) of the device and arranged or positioned to reduce orminimize the distance between the light source(s) and/or the associateddetector(s) and the skin of the user. FIG. 5 shows a cross-sectionalview of a backside sensor module for a biometric monitoring deviceaccording to one or more embodiments. For example, the sensor module 543may be part of a sensor protrusion like that shown in FIG. 4 anddescribed above. In FIG. 5 , two light sources 540 (e.g., LEDs) areplaced on either side of a photodetector 545 to enablephotoplethysmograph (PPG) sensing in accordance with the presentdisclosure. A light-blocking material 503 may be placed between thelight sources 540 and the photodetector 545 to at least partiallyprevent light from the light sources 540 from reaching the photodetector545 without first exiting the housing of the biometric monitoringdevice. In certain embodiments, a flexible transparent layer 505 may beplaced on the lower surface of the sensor module 543 to form a seal. Thetransparent layer 505 may further serve certain other functions, such aspreventing liquid from entering the device where the light sources 540or photodetectors 545 are placed. The transparent layer 505 may beformed through in-mold labeling, or other process. In certainembodiments, the light sources 540 and/or photodetector 545 may beplaced on a flexible circuit board 501.

The configuration of FIG. 5 may improve the efficiency of light fluxcoupling between the components of the optical sensor module 543 and theuser's body. For example, in one embodiment, the light source(s) 540and/or associated detector(s) 545 may be disposed on a flexible orpliable substrate. Such flexibility may allow the backside of thebiometric monitoring device, which may be made from a compliantmaterial, to at least partially conform to the shape of the body part(for example, the user's wrist, arm, ankle, and/or leg) to which thebiometric monitoring device is coupled to or attached during normaloperation, such that the light source(s) 540 and/or associateddetector(s) 545 are close to the skin of the user (i.e., with little orno gap between the skin-side of the device and the adjacent surface ofthe skin of the user.

FIG. 6 depicts a cross-sectional view of a sensor protrusion 643 of anexample wearable biometric monitoring device. In the embodiment of FIG.6 , one or more of the light sources 640 and photo detector(s) 645 maybe disposed on a flat and/or rigid circuit board (PCB).

FIGS. 7A-7C provide diagrams of physiological metric sensor componentsaccording to certain embodiments. Physiological metric sensor modules,such as optical sensor modules, in biometric monitoring devices of thepresent disclosure may employ light pipes 747 or otherlight-transmissive structures to facilitate transmission of light fromlight sources 740 to a user's body 702 and skin 701. In this regard, insome embodiments, light may be directed from the light source(s) 740 tothe skin 701 of the user through such light pipes 747 or otherlight-transmissive structures. Scattered light from the user's body maybe directed back to optical circuitry in the biometric monitoring devicethrough the same or similar structures. Indeed, the light-transmissivestructures 747 may employ a material and/or optical design to facilitatelow light loss (for example, the light-transmissive structures 747 mayinclude a lens to facilitate light collection, and portions of thelight-transmissive structures may be coated with or adjacent toreflective materials to promote internal reflection of light within thelight-transmissive structures), thereby improving thesignal-to-noise-ratio of the photo detector(s) 745 and/or facilitatingreduced power consumption of the light source(s) 740 and/or lightdetector(s) 745. In some embodiments, the light pipes 747 or otherlight-transmissive structures may include a material that selectivelytransmits light having one or more specific or predetermined wavelengthswith higher efficiency than others, thereby acting as a bandpass filter.Such a bandpass filter may be tuned to improve the signal of a specificphysiological data type. For example, in one embodiment, anIn-Mold-Labeling (IML) light-transmissive structure may be implemented,wherein the light-transmissive structure uses a material withpredetermined or desired optical characteristics to create a specificbandpass characteristic, for example, so as to pass infrared light withgreater efficiency than light of other wavelengths (for example, lighthaving a wavelength in human visible spectrum). In another embodiment, abiometric monitoring device may employ a light-transmissive structurehaving an optically opaque portion (including certain opticalproperties) and an optically-transparent portion (including opticalproperties different from the optically-opaque portion). Such alight-transmissive structure may be provided via a double-shot ortwo-step molding process wherein optically opaque material and opticallytransparent material are separately injected into a mold. A biometricmonitoring device implementing such a light-transmissive structure mayinclude different light transmissivity properties for differentwavelengths depending on the direction of light travel through thelight-transmissive structure. For example, in one embodiment, theoptically-opaque material may be reflective to a specific wavelengthrange so as to more efficiently transport light from the user's bodyback to the light detector (which may be of a different wavelength(s)relative to the wavelength(s) of the emitted light).

In certain embodiments, reflective structures may be placed in the fieldof view of the light emitter(s) 740 and/or light detector(s) 745. Forexample, the sides of the light transmission channels may be at leastpartially covered in a reflective material (e.g., chromed) to facilitatelight transmission. The reflective material may increase the efficiencywith which the light is transported to the skin 701 from the lightsource(s) 740 and then from the skin back into the detector(s) 745. Thereflectively-coated channel may be filled in with an optical epoxy orother transparent material to prevent liquid from entering the devicebody while still allowing light to be transmitted with low transmissionloss.

In certain embodiments, light-transmissive channels/structures 747 mayinclude a mask consisting of an opaque material that limits the apertureof one, some, or all of the light source(s) and/or detector(s). In thisway, the light-transmissive structures 747 may selectively define apreferential volume of the user's body that light is emitted into and/ordetected from. Notably, other mask configurations may be employed orimplemented in connection with the concepts described and/or illustratedherein that improve the photoplethysmography signal and which areimplemented in connection with the concepts described and/or illustratedherein are intended to fall within the scope of the present disclosure.

In certain embodiments, the light emitter(s) 740 and/or detector(s) 745may be configured to transmit light through a hole or series of holes inthe device exterior. This hole or series of holes may be filled in withlight-transmissive epoxy (e.g. optical epoxy). The epoxy may form alight pipe that allows light to be transmitted from the light emitter(s)to the skin and from the skin back into the light detector(s). Suchtechnique may provide the advantage that the epoxy may form a watertightseal, preventing water, sweat or other liquid from entering the devicebody though the hole(s) on the device exterior that allow the lightemitter(s) and detector(s) to transmit to, and receive light from, thebiometric monitoring device body exterior. An epoxy with a high thermalconductivity may be used to help prevent the light source(s) 745 (e.g.,LED's) from overheating.

FIG. 7A illustrates an example embodiment of a photoplethysmography(PPG) light source and photodetector geometry. In the embodiment of FIG.7A, two light sources 740 are placed on either side of a photodetector745. These three devices may be located in a protrusion form on thebackside of a wristband-type biometric monitoring device (e.g., the sidewhich faces the skin of the user), as described above.

FIGS. 7B and 7C illustrate examples of a physiological metric (e.g.,PPG) sensor having a light detector 745 (e.g., photodetector) and twolight sources 740 (e.g., LED). Such components may be disposed in abiometric monitoring device that has a protrusion form on the backside.In certain embodiments, light pipes 747 optically connect the LEDs 740and photodetector 745 with the surface of the user's skin 701. Beneaththe skin 701, the light from the light sources 740 may scatter off ofblood 703 in the body, some of which may be scattered or reflected backinto the photodetector 745.

FIG. 8 illustrates an example of a biometric monitoring device 800 withan optimized PPG detector that has a protrusion with curved sides so asnot to discomfort the user. Additionally, the surface of light pipes 847that optically couple the photodetector 845 and the LEDs 840 to thewearer's skin may be contoured to improve light flux coupling betweenthe LEDs 840 and photodetector(s) 845 and the light pipes 847. The endsof the light pipes that face the user's skin may also be contoured. Thiscontour may focus or defocus light to optimize the PPG signal. Forexample, the contour may focus emitted light to a certain depth andlocation that coincides with an area where blood flow is likely tooccur. The vertex of these foci may overlap or be very close together sothat the photodetector receives the maximum possible amount of scatteredlight.

In certain embodiments, the biometric monitoring device may include aconcave or convex shape, e.g., a lens, on the skin-side of the device,to focus light towards a specific volume at a specific depth in the skinand increase the efficiency of light collected from that point into thephotodetector. Where such a biometric monitoring device also employslight pipes to selectively and controllably route light, it may beadvantageous to shape the end of the light pipe with a degree ofcylindricity, e.g., the end of the light pipe may be a be a cylindricalsurface (or portion thereof) defined by a cylinder axis that isnominally parallel to the skin-side (for example, rather than use anaxially-symmetric lens). For example, in a wristband-style biometricmonitoring device, such a cylindrical lens may be oriented such that thecylinder axis is nominally parallel to the wearer's forearm, which mayhave the effect of limiting the amount of light that enters such a lensfrom directions parallel to the person's forearm and increasing theamount of light that enters such a lens from directions perpendicular tothe person's forearm—since ambient light is more likely to reach thesensor detection area from directions that are not occluded by thestraps of the biometric monitoring device, i.e., along the user'sforearm axis, than from directions that are occluded by the straps,i.e., perpendicular to the user's forearm. Such a configuration mayimprove the signal-to-noise-ratio by increasing the efficiency of lighttransferred from the emitter onto or into the skin of the user whiledecreasing “stray” light from being detected or collected by thephotodetector. In this way, the signal sampled, measured and/or detectedby the photodetector consists less of stray light and more of the user'sskin/body response to such emitted light (signal or data that isrepresentative of the response to the emitted light).

In one embodiment, the optical sensors (sources and/or detectors) may bedisposed on an interior or skin-side of the biometric monitoring device(i.e., a side of the biometric monitoring device that contacts, touches,and/or faces the skin of the user (hereinafter “skin-side”). (See, forexample, FIGS. 2A through 3C). In another embodiment, the opticalsensors may be disposed on one or more sides of the device, includingthe skin-side and one or more sides of the device that face or areexposed to the ambient environment (environmental side). (See, forexample, FIGS. 6A through 7 ).

FIG. 9 illustrates an example of a portable monitoring device having aband 907 with one or more optical sensors and light emitters 941disposed in association with the inside of the band. For example, theremay be a plurality of photodetectors and photo emitters placed atvarious sites along the circumference of the interior of the band 907. Aheart rate signal-quality metric associated with each site may becalculated to determine the best or set of best sites for estimating theuser's heart rate. Subsequently, some of the sites may be disabled orturned off to, for example, reduce power consumption. The device mayperiodically check the heart rate signal quality at some or all of thesites to enhance, monitor and/or optimize signal and/or powerefficiency.

FIG. 10 illustrates an example of a portable biometric monitoring device1001 having a display 1030 and wristband 1007. Additionally, optical PPG(e.g., heart rate) detection sensors and/or emitters 1041 may be locatedon the side of the biometric monitoring device. In one embodiment, thesemay be located in side-mounted buttons.

All of the optical sensors discussed herein may be used in conjunctionwith other sensors to improve detection of the data described above orbe used to augment detection of other types of physiological orenvironmental data.

FIG. 11A depicts an example schematic block diagram of an optical heartrate sensor where light is emitted from a light source toward the user'sskin and the reflection of such light from the skin/internal body of theuser is sensed by a light detector, the signal from which issubsequently digitized by an analog to digital converter (ADC). Theintensity of the light source may be modified (e.g., through a lightsource intensity control module) to maintain a desirable reflectedsignal intensity. For example, the light source intensity may be reducedto avoid saturation of the output signal from the light detector. Asanother example, the light source intensity may be increased to maintainthe output signal from the light detector within a desired range ofoutput values. Notably, active control of the system may be achievedthrough linear or nonlinear control methods such asproportional-integral-derivative (PID) control, fixed step control,predictive control, neural networks, hysteresis, and the like, and mayalso employ information derived from other sensors in the device such asmotion, galvanic skin response, etc. FIG. 11A is provided forillustration and does not limit the implementation of such a system to,for instance, an ADC integrated within a MCU, or the use of a MCU forthat matter. Other possible implementations include the use of one ormore internal or external ADCs, FPGAs, ASICs, etc.

In another embodiment, system with an optical heart rate sensor mayincorporate the use of a sample-and-hold circuit (or equivalent) tomaintain the output of the light detector while the light source isturned off or attenuated to save power. In embodiments where relativechanges in the light detector output are of primary importance (e.g.,heart rate measurement), the sample-and-hold circuit may not have tomaintain an accurate copy of the output of the light detector. In suchcases, the sample-and-hold may be reduced to, for example, a diode(e.g., Schottky diode) and capacitor. The output of the sample-and-holdcircuit may be presented to an analog signal conditioning circuit (e.g.,a Sallen-Key bandpass filter, level shifter, and/or gain circuit) tocondition and amplify the signal within frequency bands of interest(e.g., 0.1 Hz to 10 Hz for cardiac or respiratory function), which maythen be digitized by the ADC. See, for example, FIG. 11B.

In operation, circuit topologies such as those already described herein(e.g. a sample-and-hold circuit) remove the DC and low frequencycomponents of the signal and help resolve the AC component related toheart rate and/or respiration. The embodiment may also include theanalog signal conditioning circuitry for variable gain settings that canbe controlled to provide a suitable signal (e.g., not saturated). Theperformance characteristics (e.g., slew rate and/or gain bandwidthproduct) and power consumption of the light source, light detector,and/or sample-and-hold may be significantly higher than the analogsignal conditioning circuit to enable fast duty cycling of the lightsource. In some embodiments, the power provided to the light source andlight detector may be controlled separately from the power provided tothe analog signal conditioning circuit to provide additional powersavings. Alternatively, or additionally, the circuitry can usefunctionality such as an enable, disable and/or shutdown to achievepower savings. In another embodiment, the output of the light detectorand/or sample-and-hold circuit may be sampled by an ADC in addition toor in lieu of the analog signal conditioning circuit to control thelight intensity of the light source or to measure the physiologicparameters of interest when, for example, the analog signal conditioningcircuit is not yet stable after a change to the light intensity setting.Notably, because the physiologic signal of interest is typically smallrelative to the inherent resolution of the ADC, in some embodiments, thereference voltages and/or gain of the ADC may be adjusted to enhancesignal quality and/or the ADC may be oversampled. In yet anotherembodiment, the device may digitize the output of only thesample-and-hold circuit by, for example, oversampling, adjusting thereference voltages and/or gain of the ADC, or using a high resolutionADC. See, for example, FIG. 11C.

in some embodiments, the color or wavelength of the light emitted by thelight source, e.g., an LED (or set of LEDs), may be modified, adjusted,and/or controlled in accordance with a predetermined type ofphysiological data being acquired or conditions of operation. Here, thewavelength of the light emitted by the light source may be adjustedand/or controlled to optimize and/or enhance the “quality” of thephysiological data obtained and/or sampled by the detector. For example,the color of the light emitted by the LED may be switched from infraredto green when the user's skin temperature or the ambient temperature iscool in order to enhance the signal corresponding to cardiac activity.(See, for example, FIG. 11D)

Ambient Light Determination

In another embodiment, the sensor device may incorporate a differentialamplifier to amplify the relative changes in the output of the lightdetector. See, for example, FIG. 11F. In some embodiments, a digitalaverage or digital low-pass filtered signal may be subtracted from theoutput of the light detector. This modified signal may then be amplifiedbefore it is digitized by the ADC. In another embodiment, an analogaverage or analog low-pass filtered signal may be subtracted from theoutput of the light detector through, for example, the use of asample-and-hold circuit and analog signal conditioning circuitry. Thepower provided to the light source, light detector, and differentialamplifier may be controlled separately from the power provided to theanalog signal conditioning circuit to improve power savings.

In another embodiment, a signal (voltage or current, depending on thespecific sensor implementation) may be subtracted from the raw PPGsignal to remove any bias in the raw PPG signal and therefore increasethe gain or amplification of the PPG signal that contains heart rate (orother circulatory parameters such as heart rate variability)information. This signal may be set to a default value in the factory,to a value based on the user's specific skin reflectivity, absorption,and/or color, and/or may change depending on feedback from an ambientlight sensor, or depending on analytics of the PPG signal itself. Forexample, if the PPG signal is determined to have a large DC offset, aconstant voltage may be subtracted from the PPG signal to remove the DCoffset and enable a larger gain, therefore improving the PPG signalquality. The DC offset in this example may result from ambient light(for example from the sun or from indoor lighting) reaching thephotodetector from or reflected light from the PPG light source.

In another embodiment, a differential amplifier may be used to measurethe difference between current and previous samples rather than themagnitude of each signal. Since the magnitude of each sample istypically much greater than the difference between each sample, a largergain can be applied to each measurement, therefore improving the PPGsignal quality. The signal may then be integrated to obtain the originaltime domain signal.

In another embodiment, the light detector module may incorporate atransimpedance amplifier stage with variable gain. Such a configurationmay avoid or minimize saturation from bright ambient light and/or brightemitted light from the light source. For example, the gain of thetransimpedance amplifier may be automatically reduced with a variableresistor and/or multiplexed set of resistors in the negative feedbackpath of the transimpedance amplifier. In some embodiments, the devicemay incorporate little to no optical shielding from ambient light byamplitude-modulating the intensity of the light source and thendemodulating the output of the light detector (e.g., synchronousdetection). See, for instance, FIG. 11E. In other aspects, if theambient light is of sufficient brightness to obtain a heart rate signal,the light source may be reduced in brightness and/or turned offcompletely.

In yet another embodiment, the aforementioned processing techniques maybe used in combination to optically measure physiological parameters ofthe user. See, for example, FIG. 11G. This topology may allow the systemto operate in a low power measurement state and circuit topology whenapplicable and adapt to a higher power measurement state and circuittopology as necessary. For instance, the system may measure thephysiologic parameter (e.g., heart rate) of interest using analogsignal-conditioning circuitry while the user is immobile or sedentary toreduce power consumption, but switch to oversampled sampling of thelight detector output directly while the user is active.

Circuits for Performing PPG

PPG circuitry may be optimized to obtain the best quality signalregardless of a variety of environmental conditions including, but notlimited to, motion, ambient light, and skin color. The followingcircuits and techniques may be used to perform such optimization (seeFIGS. 12A through 12J); a sample-and-hold circuit anddifferential/instrumentation amplifier which may be used in PPG sensing.The output signal is an amplified difference between current andprevious sample, referenced to a given voltage. controlled currentsource to offset “bias” current prior to transimpedance amplifier. Thisallows greater gain to be applied at transimpedance amplifier stage. asample-and-hold circuit for current feedback applied to photodiode(prior to transimpedance amplifier). This can be used for ambient lightremoval, or “bias” current removal, or as a pseudo differentialamplifier (may require dual rails). a differential/instrumentationamplifier with ambient light cancellation. a photodiode offset currentgenerated dynamically by a DAC. a photodiode offset current generateddynamically by controlled voltage source. ambient light removal using a“switched capacitor” method. photodiode offset current generated by aconstant current source (also can be done with a constant voltage sourceand a resistor). ambient light removal and differencing betweenconsecutive samples. ambient light removal and differencing betweenconsecutive samples.

FIG. 12A illustrates an example schematic of a sample-and-hold circuitand differential/instrumentation amplifier which may be used in PPGsensing. The output signal in such a circuit may be an amplifieddifference between a current sample and a previous sample, referenced toa given voltage.

FIG. 12B illustrates an example schematic of a circuit fora PPG sensorusing a controlled current source to offset “bias” current prior to atransimpedance amplifier. This allows greater gain to be applied at thetransimpedance amplifier stage.

FIG. 12C illustrates an example schematic of a circuit fora PPG sensorusing a sample-and-hold circuit for current feedback applied tophotodiode (prior to a transimpedance amplifier). This circuit may beused for ambient light removal, or “bias” current removal, or as apseudo-differential amplifier.

FIG. 12D illustrates an example schematic of a circuit fora PPG sensorusing a differential/instrumentation amplifier with ambient lightcancellation functionality.

FIG. 12E illustrates an example schematic of a circuit fora PPG sensorusing a photodiode offset current generated dynamically by a DAC.

FIG. 12F illustrates an example schematic of a circuit for a PPG sensorusing a photodiode offset current generated dynamically by a controlledvoltage source.

FIG. 12G illustrates an example schematic of a circuit for a PPG sensorincluding ambient light removal functionality using a “switchedcapacitor” method.

FIG. 12H illustrates an example schematic of a circuit fora PPG sensorthat uses a photodiode offset current generated by a constant currentsource (this may also be done using a constant voltage source and aresistor).

FIG. 12I illustrates an example schematic of a circuit for a PPG sensorthat includes ambient light removal functionality and differencingbetween consecutive samples.

FIG. 12J illustrates an example schematic of a circuit for ambient lightremoval and differencing between consecutive samples.

Various circuits and concepts related to heart rate measurement using aPPG sensor are discussed in more detail in U.S. Provisional PatentApplication No. 61/946,439, filed Feb. 28, 2014 which is herebyincorporated by reference with respect to content directed at heart ratemeasurements with a PPG sensor and at circuits, methods, and systems forperforming such measurements.

FIG. 13 shows an example light emission driver circuit 440 for driving alight emitter to emit an incident light signal L_(E) onto a region ofthe skin of a user according to some implementations. For example, thelight emission driver circuit 440 can be used in conjunction with theany light source of a biometric monitoring device of the presentdisclosure. As described above, a portion of the incident light signalL_(E) is reflected, refracted, or otherwise scattered by the skin of theuser, and more particularly, the arteries below the skin of the user.The portion of the incident light scattered by the skin of the user alsois referred to herein as the “scattered light signal” L_(S). FIG. 14shows a block diagram of an example light detection circuit 560 fordetecting the scattered light signal L_(S) and for outputting an outputsignal OUT based on the scattered light signal L_(S) according to someimplementations. For example, the light detection circuit 560 can beused in conjunction with any of the light detectors of physiologicalmetric sensor modules of the present disclosure. FIG. 15 shows anexample circuit 660 for implementing the light detection circuit 560 ofFIG. 14 according to some implementations.

The light emission driver circuit 440 includes, at a high level, avoltage-controlled current source that drives a light emitter 442arranged to emit an incident light signal L_(E) onto a region of theskin of a user. For example, the light emitter 442 can be the lightemitter 336 described above and, as described above, can include one ormore LEDs, laser, or other light sources. In the illustratedimplementation, the voltage-controlled current source is implemented bya driver circuit 444 that powers the light emitter 442 based on one ormore control signals Cntrl_(D) received from, for example, theprocessing unit 104. In some implementations, the driver circuit 44 isconfigured to drive (or “power”) the light emitter 442 for certainintervals of time based on the control signals Cntrl_(D) (for example,when enabled by a control signal) such that the light emitter 442 emitsa light signal L_(E) in the form of a series (or “train”) of pulsesduring the intervals of time. For example, in some cases, the lightemitter 442 may be a relatively costly component of the portablemonitoring device 100 in terms of power consumption. Thus, it may bedesirable to power the light emitter 442 for only a short amount oftime, hence the use of a series of short pulses.

While other implementations of a driver circuit 444, including otherimplementations of a voltage-controlled current source, are within thescope of this disclosure, in the illustrated implementation the drivercircuit 444 includes an operational amplifier 446 having a first inputterminal, a second input terminal and an output terminal. The drivercircuit also includes a digital to analog converter (DAC) 448electrically coupled with the first input terminal of the operationalamplifier 446. The DAC 448 provides an input signal V_(IN) to the firstinput terminal of the operational amplifier 446 based on a referencesignal V_(REF) and the control signals Cntrl_(D). A power supply railsupplies a power source to a first terminal of the light emitter 442.

The driver circuit 440 may also include a switch, and more particularly,a transistor 450. In the illustrated implementation, the transistor 450may be a metal-oxide-semiconductor field-effect transistors (MOSFET),such as an n-channel MOSFET (an “NMOS transistor”). In some otherimplementations, the transistor 450 may be implemented by another typeof switch or transistor such as, for example, a bipolar junctiontransistor. The transistor 450 includes a gate terminal, a drainterminal D and a source terminal S. In certain embodiments, the gateterminal may be electrically coupled with the output terminal of theoperational amplifier 446. The drain terminal D may be electricallycoupled with a second terminal of the light emitter 442. The sourceterminal S may be electrically coupled, via a resistor 452 having aresistance R_(S), to a reference voltage, such as a ground. The sourceterminal S may be further electrically coupled with the second inputterminal of the operational amplifier 446 for providing a feedbacksignal to the operational amplifier. In the illustrated implementation,the driver circuit 444 further includes a capacitor 454 having acapacitance C_(P) electrically coupled between the output terminal ofthe operational amplifier 446 and the second input terminal of theoperational amplifier. The driver circuit 444 also can include aresistor 456 having a resistance R_(P1); between the output terminal ofthe operational amplifier 446 and the gate terminal of the transistor450. The driver circuit 444 also can include a resistor 458 having aresistance R_(P2); between the source terminal S of the transistor 450and the second input terminal of the operational amplifier 446. Theresistances R_(P1); and R_(P2); and the capacitance C_(P) can beconfigured to tune the driver circuit 444 to obtain fast settling times,which can save power because can be operated for less time, whilemaintaining stability. During operation, the operational amplifier 446may be configured to, based on the feedback signal received at thesecond input terminal of the operational amplifier, maintain asubstantially constant voltage across the resistor 452. In this way, thedriver circuit 444 behaves as a constant current source with a currentI_(E)=V_(IN)/R_(S) passing through the light emitter 442 and resistor452. This may be desirable because any change or ripple in the currentI_(E) provided to the light emitter 452 will result in undesiredartifacts in the incident light signal L_(E), which will also show inthe scattered light signal L_(S).

Referring now to FIG. 14 , the light detection circuit 560 may beconfigured to detect a scattered light signal L_(S), (for example, aportion of the incident light signal L_(E) scattered by the skin of theuser), generate a detected electrical signal I_(D) based on thescattered light signal, sample the electrical signal to generate asampled signal S₁, and digitize the sampled signal to generate an outputsignal OUT that represents, for example, heart rate data. As describedabove, ambient light conditions, skin color (pigmentation) and usermotion all can make it difficult to extract a user's heart rate fromdata signal. In some implementations, the light detection circuit 560may be configured to correct for a low frequency or “DC” offsetresulting from ambient light. For example, ambient light conditions canchange as a user moves or changes orientation (for example, hand orbody) or as external lighting conditions (for example, sun light orinterior lighting) change over time. In some implementations, the lightdetection circuit 560 may be configured to correct for ambient lightconditions by effectively subtracting an ambient light component of thedetected signal I_(D) obtained when a light source (for example, thelight emitter 334) may be off from the detected signal when the lightsource may be on and the signal may be to be sampled.

In some implementations, the light detection circuit 560 also may beconfigured to adjust a gain of the detected signal I_(D) to preventsaturation of various electrical components (for example, operationalamplifiers) of the light detection circuit 560 or to bring the values ofthe sampled signal S₁ into a range that may be suitable for an ADC thatdigitizes the sampled signal to generate the output signal OUT. Forexample, because the time-varying “AC” component of the scattered lightsignal L_(S) due to the user's cardiac output can be relatively small incomparison to the low frequency or “DC” component due to ambient light,and because it may be desirable to use high frequency short pulses toreduce the power consumption of the light emitter 442, it may bedesirable to subtract the DC ambient light component prior to thesampled signal reaching the ADC. More specifically, if the DC ambientcomponent is not subtracted, the ADC may not be able to takemeasurements/receive data at the speed for which it may be desired topulse the emitted light because the detected signal may be so large thatthe ADC can't resolve the desired AC component at the desired bit depthin the short time required (for example, high precision/high bit depthADCs tend to be slow because of the processing requirements).Additionally, it can be advantageous to for the light detection circuit560 to adjust the gain of the detected light signal I_(D) to account fordifferences in users' skin tones (pigmentations). For example, differentskin tones will absorb and scatter light differently. For example,because darker skin tones can absorb more light and scatter less light,it can be desirable to increase the gain of the detected light signalI_(D).

The light detection circuit 560 includes a light detector 562 positionedand configured to receive (or “sense” or “detect”) at least a portion ofthe scattered light signal L_(S) and to generate the detected electricalsignal I_(D) based on the received light. In some implementations, thelight detector 562 may be configured to generate the first electricalsignal I_(D) in the form of a time-varying current signal. In suchimplementations, the magnitude of the current in the first electricalsignal I_(D) may be proportional to the intensity of the scattered lightsignal L_(S) (and ambient light) currently being received by the lightdetector 562 in its detectable range of wavelengths. In some otherimplementations, the light detector 562 can be configured to generatethe first electrical signal I_(D) in the form of a time-varying voltagesignal. In such implementations, the magnitude of the voltage in thefirst electrical signal I_(D) would be proportional to the intensity ofthe scattered light signal L_(S) (and ambient light) currently beingreceived by the light detector in its detectable range of wavelengths.

In accordance with certain embodiments, where the generated electricalsignal I_(D), or other signal derived at least in part therefrom, isrepresentative of detected light while the light emitter 442 (see FIG.13 ) is off, such signal may be analyzed or otherwise utilized to makean ambient lighting condition determination upon which displaybrightness level setting modification for an associated electronicdisplay is based.

The light detection circuit 560 may also include a switching circuit564. The switching circuit 564 can be implemented using a variety ofsuitable switching technologies including one or more analog or digitalswitching elements. For example, in some implementations, the switchingcircuit 564 includes an analog integrated circuit. In someimplementations, the first switching circuit 564 may be comprised of oneor more transistors, such as, for example, one or more pairs of MOSFETs(for example, where each pair includes an NMOS device and a P-channelMOSFET (PMOS) device). In various implementations, the switching circuit564 includes at least a first configuration a and a second configurationb (in some implementations, the switching circuit 564 also includes athird configuration c). The switching circuit 564 may be configured toreceive a voltage signal V_(S) that may be based on the detected signalI_(D), as described in more detail below. The switching circuit 564 alsomay be configured to receive one or more first control signals Cntrl₁received from, for example, the processing unit 104. The switchingcircuit 564 switches among at least the first configuration a and thesecond configuration b based on the one or more first control signalsCntrl₁.

The light detection circuit 560 also includes a first sampling circuit566 configured to sample a value of the voltage signal V_(S) when theswitching circuit 564 may be in the first configuration a. The lightdetection circuit 560 also includes a second sampling circuit 568configured to sample a value of the voltage signal V_(S) when the firstswitching circuit 564 may be in the second configuration b.

The light detection circuit 560 may also include an adjustable gaincircuit 570 configured to provide (or “output” or “set”) a signal I₁(for example, a current signal) to adjust a gain of the voltage signalV_(S) relative to the detected signal I_(D) when the first switchingcircuit 564 may be in the first configuration. As described above, itcan be desirable to adjust the gain so that the light detection circuit560 can accurately and reliably detect the scattered light signal L_(S)so that, for example, an analog-to-digital converter (ADC) 576 canresolve a digital signal from the sampled signal S₁. In can additionallybe desirable to adjust the gain so that other components of the lightdetection circuit 560 (for example, operational amplifiers) don'tsaturate or otherwise function improperly or undesirably. The adjustablegain circuit 570 sets the magnitude and polarity of the current signalbased on one or more second control signals Cntrl₂ (received from, forexample, the processing unit 104) and based (directly or indirectly) onthe value of the detected signal I_(D) as described in more detailbelow.

The light detection circuit 560 also includes an ambient lightcancellation circuit 572 configured to provide a countering currentsignal I₂ to at least partially counter an undesired component of thedetected signal I_(D) when the switching circuit 564 may be in the firstconfiguration. The ambient light cancellation circuit 572 sets themagnitude and polarity of the current signal I₂ based on one or morethird control signals Cntrl₃ (received from, for example, the processingunit 104) and based on the value of the signal S₂ (for example, avoltage signal) sampled by the second sampling circuit 568, as describedin more detail below. For example, as described above, the component ofthe detected signal I_(D) to be canceled can be the result of ambientlight. That may be, the light detector 562 can receive ambient light inaddition to the time-varying scattered light signal L_(S), and as aresult, the detected signal I_(D) can include an ambient component inadditional to the time-varying component resulting from the scatteredlight signal L_(S) (It should be noted that, although the ambient lightcomponent can vary with time as well, such an ambient light timevariance may be of a relatively much lower frequency and effectively“DC” or “static” when compared with the frequency of the time-varyingincident light signal L_(E) and the sampling rate of the first andsecond sampling circuits 566 and 568, respectively). In someimplementations, the light detection circuit 560 also may be configuredto adjust a gain of the detected signal I_(D) to prevent saturation ofvarious electrical components (for example, operational amplifiers) ofthe light detection circuit 560 or to bring the values of the sampledsignal S₁ into a range that may be suitable for the ADC 576.

As described above, in some implementations, the light detector 562 maybe configured to output the detected signal I_(D) as a time-varyingcurrent signal. In such implementations, the light detection circuit 560can further include an electrical current-to-voltage converter 574configured to convert the detected signal I_(D) to a voltage signalV_(G). In such implementations, the adjustable gain circuit 570 morespecifically sets the current signal I₁ to adjust a gain of the voltagesignal V_(G) relative to the first electrical signal I_(D) when thefirst switching circuit 564 may be in the first configuration.Additionally, in such implementations, the magnitude and polarity of thecurrent signal I₁ are more specifically based on the second controlsignals Cntrl₂ and the voltage signal V_(G).

In some implementations, the light detection circuit 560 also includes abuffer 578 that buffers the voltage signal V_(G) and outputs buffersignal V_(S). The light detection circuit 560 also can include a buffer580 that buffers the sampled signal S₁ prior to input into the ADC 576.The light detection circuit 560 also can include a buffer 582 thatbuffers the sampled signal S₂ prior to input into the ambient lightcancellation circuit 572.

In some implementations, the components of the current-to-voltageconverter 574 and the adjustable gain circuit 570 form or function as atransimpedance amplifier 584 with variable gain. As described above,such a configuration can avoid or minimize saturation from brightambient light or bright incident light from the light emitter. Forexample, as described in more detail below, the gain of thetransimpedance amplifier 584 may be automatically increased or decreasedwith a variable resistors or a multiplexed set or network of resistorsin the negative feedback path of the transimpedance amplifier. FIG. 15shows an example circuit 660 for implementing the light detectioncircuit 560 of FIG. 14 according to some implementations. For example,the current-to-voltage converter 574 can include a first operationalamplifier 674. A first input terminal of the operational amplifier 674can be electrically coupled with a first terminal of the light detector652 (for example, a photodiode) and a first terminal T₁ of an adjustableimpedance stage 670. A second input terminal of the operationalamplifier 674 can be electrically coupled with a reference voltage, suchas a ground. In the circuit 660, the adjustable gain circuit 570includes an adjustable impedance stage 670, which may be configured toprovide an adjustable impedance. The output terminal of the operationalamplifier 674 can be electrically coupled with a second terminal T₂ ofthe adjustable impedance stage 670. The output terminal of theoperational amplifier 674 also outputs the voltage signal V_(G). Asdescribed above, the operational amplifier 674 and the adjustableimpedance stage 670 form or function as a transimpedance amplifier 684.

In the example implementation, the adjustable impedance stage 670includes an impedance network having a first impedance path 673 aincluding a resistor having a resistance R₁ and a capacitor having acapacitance C₁ that provide a first impedance. The impedance networkalso includes a second impedance path 673 b including a resistor havinga different resistance R₂ and a capacitor having a capacitance C₂ thatprovide a second impedance. The adjustable impedance stage 670 furtherincludes a second switching circuit 671 configured to transition betweena first configuration d and a second configuration e to select among thefirst impedance path 673 a and the second impedance path 673 b,respectively, based on the one or more second control signals Cntrl₂. Itshould be appreciated that although the circuit 660 includes only twoimpedance paths, in some other implementations three or more impedancepaths can be included and the second switching circuit 671 can selectamong the three or more impedance paths. Additionally, in some otherimplementations, rather than having an impedance network having multiplepaths of different impedance, the adjustable impedance stage can includea variable impedance, such as an analog component configured to vary animpedance to vary the gain.

In the circuit 660, the ambient light cancellation circuit 572 includesa second adjustable impedance stage 672 between a first terminal T₃ ofthe ambient light cancellation circuit 572 and a second terminal T₄ ofthe ambient light cancellation circuit 572. The second adjustableimpedance stage 672 may be configured to provide an adjustable impedanceto adjust the current signal I₂. In the example implementation, theadjustable impedance stage 672 includes an impedance network having afirst impedance path 677 a including a resistor having a resistance R₁.The impedance network also includes a second impedance path 677 bincluding a resistor having a different resistance R₂. The adjustableimpedance stage 672 further includes a third switching circuit 675configured to transition between a first configuration d and a secondconfiguration e to select among the first impedance path 677 a and thesecond impedance path 677 b based on the one or more third controlsignals Cntrl₃.

Notably, in some implementations, the resistances in the impedance paths673 a and 677 a are the same (R₁) while the resistances in the impedancepaths 673 b and 677 b are the same (R₂). That is, in someimplementations, for each impedance path in the adjustable impedancestage 670 of the adjustable gain circuit 570 there may be acorresponding impedance path in the adjustable impedance stage 672 ofthe ambient light cancellation circuit 572 having the same resistance.Thus, in some implementations, when the second switching circuit 671 maybe in configuration d, the third switching circuit 675 also may be inconfiguration d, and similarly, when the second switching circuit 671may be in configuration e, the third switching circuit 675 also may bein configuration e. In some implementations, the second switchingcircuit 671 and the third switching circuit 675 can include the sameswitching elements or be a part of a single switch (for example, asingle analog switch) that controls both the impedance stage 670 and theimpedance stage 672. In such implementations, the third control signalsCntrl₃ can be the second control signals Cntrl₂.

Additionally, as described above with reference to the adjustableimpedance stage 670 of the adjustable gain circuit 570, in some otherimplementations, rather than having an impedance network having multiplepaths of different impedance, the adjustable impedance stage 672 of theambient light cancellation circuit 572 can include a variable impedance,such as an analog component configured to vary an impedance.

In the circuit 660, the buffer 578 includes a second operationalamplifier 678. A first input terminal of the second operationalamplifier 678 may be electrically coupled with the output terminal ofthe operational amplifier 674. The output terminal of the secondoperational amplifier 678 may be electrically coupled with the secondinput terminal of the second operational amplifier. In someimplementations, the circuit further includes an isolation resistor 686,having a resistance R_(ISO), electrically coupled in series between theoutput terminal of the second operational amplifier 678 and theswitching circuit 564. For example, the isolation resistor 686 can serveas a dampening mechanism to minimize ringing.

The first sampling circuit 566 includes a first sample-and-hold (S/H)circuit configured to receive the voltage signal V_(S), sample a valueof the voltage signal V_(S), and hold (or “maintain,” “capture,” or“store”) the sampled value S₁ for a time interval in between consecutivesamples. In the circuit 660, the first S/H circuit may be implemented bythe switching circuit 564 and a capacitor 666 having a capacitanceC_(S1). For example, a first terminal of the capacitor 666 can beelectrically coupled to the switching circuit 564 to receive the voltagesignal V_(S) when the switching circuit 564 may be in the firstconfiguration a. The second terminal of the capacitor 666 can beelectrically coupled with a reference voltage, such as a ground. Whenthe switching circuit 564 transitions from the first configuration a to,for example, the second configuration b or a third configuration c, thecapacitor 666 holds the sampled value S₁. In some implementations, itmay be desirable to have a large capacitance C_(S1) so that thecapacitor 666 may be able to store a lot of charge without leakingappreciably.

In some implementations, because it may be desirable to have a largecapacitance C_(S1) (and a large capacitance C_(S2) as described below),it may be desirable to include the first buffer 578, and specificallythe operational amplifier 678, to drive the large capacitance of thecapacitor 666 (and the capacitor 668 described below). In this way, thefirst operational amplifier 574 may not have to drive any capacitors andthe performance of the operational amplifier 678 may be improved, whichcould otherwise be destabilized if required to drive a largecapacitance.

The ADC 576 may be configured generate and output a digital voltagesignal OUT based on the sampled signal S₁. As described above, in someimplementations, the light detection circuit 560 includes a secondbuffer 580 for buffering the sampled signal S₁. For example, the secondbuffer 580 can reduce or prevent instability or leakage that may becaused by the ADC 576. In some such implementations, the second buffer580 includes a third operational amplifier 680. For example, the firstinput terminal of the third operational amplifier 680 can beelectrically coupled to an output of the first sampling circuit 566—thefirst terminal of the capacitor 666. The output terminal of the thirdoperational amplifier 680 can be electrically coupled with the secondinput terminal of the third operational amplifier and with the ADC 576.

The second sampling circuit 568 may include a second sample-and-hold(S/H) circuit configured to receive the voltage signal V_(S), sample avalue of the voltage signal VS, and hold the sampled value S₂ for a timeinterval in between consecutive samples. In the circuit 660, the secondS/H circuit may be implemented by the switching circuit 564 and acapacitor 668 having a capacitance C_(S2). For example, a first terminalof the capacitor 668 can be electrically coupled to the switchingcircuit 564 to receive the voltage signal V_(S) when the switchingcircuit 564 may be in the second configuration b. The second terminal ofthe capacitor 668 can be electrically coupled with a reference voltage,such as a ground. When the switching circuit 564 transitions from thesecond configuration b to, for example, the first configuration a or athird configuration c, the capacitor 668 holds the sampled value S₂.Similar to the first sampling circuit 566, in some implementations, itmay be desirable to have a large capacitance C_(S2) so that thecapacitor 668 may be able to store a lot of charge without leakingappreciably.

As described above, in some implementations, the light detection circuit560 includes a third buffer 582 for buffering the sampled signal S₂before it may be received by the ambient light cancellation circuit 572,and in the implementation of FIG. 15 , by the adjustable impedance stage672. In some such implementations, the third buffer 582 includes afourth operational amplifier 682. For example, the first input terminalof the fourth operational amplifier 682 can be electrically coupled toan output of the second sampling circuit 568—the first terminal of thecapacitor 668. The output terminal of the fourth operational amplifier682 can be electrically coupled with the second input terminal of thefourth operational amplifier. The output terminal of the fourthoperational amplifier 682 also may be electrically coupled with theambient light cancellation circuit 572, and more specifically, theadjustable impedance stage 672. In some implementations, the thirdbuffer 582, and more specifically the fourth operational amplifier 682,may be configured to output the sampled signal S₂, and more particularlythe charge stored on the capacitor 668 associated with the value of thesampled signal S₂, to the adjustable impedance stage 672 only when anenable signal EN may be asserted or received. For example, in someimplementations, the enable signal EN may be asserted at least duringthe time interval during which the switching circuit 564 may be in thefirst configuration a. In this way, while the switching circuit 564 maybe in the first configuration a, the charge stored on the capacitor 668may be transferred in the form of electrical current to the adjustableimpedance stage 672 of the ambient light cancellation circuit 572 whereit passes through one of the impedance paths 677 a or 677 b selected bythe third switching circuit 675 and results in the current I₂ describedabove.

In some implementations, the circuit 660 further includes a fourthswitching circuit 688 coupled with the first terminal of the lightdetector 562. The fourth switching circuit 688 can be configured toelectrically couple the first terminal of the light detector 562 to avoltage reference, such as a ground, based on one or more fourth controlsignals Cntrl₄ (received from, for example, the processing unit 104). Inthis way, for example, while the light detection circuit 560/660 may benot sampling the detected light signal I_(D), such as when the switchingcircuit 564 may be in the second configuration b or the thirdconfiguration c, the charge accumulating on the light detector 562 as aresult of receiving ambient light can be drained off. In some otherimplementations, it can be useful for the fourth switching circuit 688to electrically couple the light detector 562 to a non-ground referencevoltage, such as, for example, in implementations in which it may bedesirable to reverse bias the light detector 562 (for example, toreverse bias a photodiode).

An example three-stage cycle of operation of the light emission drivercircuit 440 and the light detection circuit 560 (and 660) will now bedescribed. It should be appreciated that the stages of the example cyclecan encompass intervals of time (as opposed to discreet time points)involving multiple operations or reconfigurations, and can beoverlapping with one another in some implementations. In a first stageof operation, the one or more control signals Cntrl_(D) cause the drivercircuit 444 to drive the light emitter 442 to emit the incident lightsignal L_(E). Also in the first stage, the one or more first controlsignals Cntrl₁ cause the switching circuit 564 to transition to thefirst configuration a to enable the first sampling circuit 566 to samplea detected signal I_(D) (or more specifically a signal derived from thedetected signal I_(D) such as the signal V_(G) or V_(S)) andsubsequently, to enable the ADC 576 to digitize the sampled signal S₁and to output the output signal OUT (including, for example, heart ratedata). Also in the first stage, the one or more second control signalsCntrl₂ cause the adjustable gain circuit 670 to adjust or select animpedance and to generate the signal I₁ to adjust the gain of thevoltage signal V_(S) relative to the detected signal I_(D). Also atstage 702, the enable signal EN may be asserted causing the chargestored by the second sampling circuit 582 to be transferred via electriccurrent to the ambient light cancellation circuit 572. In response tothe one or more third control signals Cntrl₃, the ambient lightcancellation circuit 572 adjusts or selects an impedance and generatesthe cancelling signal I₂ based on the charge received from the secondsampling circuit 582 to cancel (or counter) an ambient component of thedetected signal I_(D). Also in the first stage, the one or more fourthcontrol signals Cntrl₄ cause the fourth switching circuit 688 todecouple the light detector 562 from the reference voltage such that thelight detector 562 can generate the detected signal I_(D).

In some implementations, in a second stage of operation, the one or morefirst control signals Cntrl₁ cause the switching circuit 564 totransition to the second configuration b to disable the first samplingcircuit 566 and to enable the second sampling circuit 568 to sample thedetected signal I_(D) while the light emitter 442 may be off to, forexample, store a charge proportional to an ambient component of thedetected signal I_(D). Also in the second stage, the enable signal ENmay be de-asserted to enable the second sampling circuit 582 to storecharge (for example, on capacitor 668) associated with the sampledsignal S₂. As described above, it may be the charge associated with thesampled signal S₂ that may be later used to provide the signal I_(D) tocancel the ambient component of the detected light signal during thefirst stage of operation.

In some implementations, in a third stage of operation, the one or morefourth control signals Cntrl₄ cause the fourth switching circuit 688 tocouple the light detector 562 to the reference voltage (for example, aground) such that the charge that would otherwise accumulate in thelight detector 562 due to ambient light can be drained away. In someimplementations, the light emission driver circuit 440 and the lightdetection circuit 560 then repeat the first stage of operation, and soon.

Additional embodiments and details relating to photoplethysmographycircuits are disclosed in U.S. patent application Ser. No. 15/223,589,entitled “Circuits and Methods for Photoplethysmographic Sensor,” filedon Jul. 29, 2016, the disclosure of which was incorporated by referencein its entirety above.

Display Brightness Level Setting Adjustment

In certain embodiments, the brightness of an electronic display of abiological monitoring device can be adjusted using the ambient lightreadings from a light detector associated with an optical physiologicalmetric sensor module, such as a phytoplethysmograph (PPG) signal on awrist worn device. For example, readings from a photodetector that areutilized for PPG generation may be converted to a common referenceframe. Such leveraging of existing PPG circuitry and/or components maybe more rudimentary than a dedicated front-side ambient light sensor,but may nevertheless provide adequate measurement of lightingconditions. In certain embodiments, ambient data from a PPG sensor maybe sufficient for detecting the difference in lighting conditionsbetween indoor and outdoor environments. Therefore, biometric monitoringdevices in accordance with the present disclosure can be configured toadjust electronic display brightness settings between at least indoorand outdoor modes, thereby resulting in power savings and extendingbattery life for the biometric monitoring device.

Generally, electronic displays may be tuned for external visibility incertain devices. For example, the display brightness level may be tunedto have different settings for inside versus outside lightingconditions. In certain embodiments, biometric monitoring devices inaccordance with the present disclosure are configured to implement athree-mode brightness level scheme, with low-, intermediate-, andhigh-light settings. Wherein a PPG sensor is designed to modify detectedlight signals to account for factors having an effect on PPGcalculations/determinations, such modifications may be substantiallyundone for the purpose of making ambient lighting determinations fordisplay brightness level management. Alternatively, the light detectorsignal may be obtained by the display brightness level managementcircuitry before it is processed/modified by the PPG circuitry. Incertain embodiments, the display brightness level management circuitrymay utilize the modified/processed PPG signals for the purpose ofobtaining a more complex solution. In certain embodiments, the displaybrightness level management and/or PPG circuitry may utilize hysteresisinformation in processing light detector signals to improve the qualityof determinations based thereon.

With further reference back to FIGS. 2 and 3 , biometric monitoringdevices in accordance with the present disclosure may include anelectronic display 230 with a configurable brightness setting. Incertain embodiments, the biometric monitoring device 200 is configuredto leverage ambient light signals from the optical physiological metricsensor module 243 associated with a backside of the biometric monitoringdevice 200 to detect indoor/outdoor ambient lighting conditions, therebyallowing for the brightness of the display 230 to be decreased orincreased in accordance therewith. In certain embodiments, the display230 is an organic light-emitting diode (OLED) display. In certainembodiments, display brightness level adjustment based on backsideambient light detection may provide reduced power consumption by up to50% or more when the display 230 is on and the user is indoors. Suchsavings may be achieved without the benefit of a front-side dedicatedambient light sensor component, which would generally be associated withincreased price, complexity, and battery consumption. Biometricmonitoring devices employing display brightness level adjustment inaccordance with the present disclosure may further provide an improveduser viewing experience compared to displays that always display at amaximum brightness setting, even when used indoors.

The display 230 of FIG. 2 may be representative of an embodiment of theelectronic display 130 of FIG. 1 , and the biometric monitoring device200 may be an embodiment of the biometric monitoring device 100. Withreference to FIG. 1 , the biometric monitoring device 100 includes abrightness level management system 113, which may be configured toadjust a brightness level setting for the electronic display 130. Asdescribed above, it may be desirable for the brightness level managementmodule 111 of the control circuitry 110 to adjust the brightness levelsetting of the electronic display 130 according to an intensity of theenvironmental ambient light. In certain embodiments, when the ambientlight is not greater than a first threshold level, the brightness levelmanagement module 111 may maintain the brightness level setting at a lowlevel. In certain embodiments, when the ambient light falls between thefirst threshold level and a second threshold level, the brightness levelsetting may be set to an intermediate level. In certain embodiments,when the ambient light is greater than the second threshold, thebrightness level setting may be set to a high level. In certainembodiments, only a single ambient light threshold is used, whereinsetting the brightness level setting involves setting the brightnesslevel to one of two settings, namely a low mode setting and a high modesetting.

In certain embodiments, the optical physiological metric sensor of thebiometric monitoring device runs substantially continuously. Indetermining the heart rate parameter(s) and/or other physiologicalmetric(s), the optical physiological metric sensor system may makeambient light determinations at any point, or in connection with anyprocess or functionality. For example, in certain embodiments, theoptical physiological metric sensor components may be configured to takeambient light readings when the light sources and/or physiologicalmetric (e.g., heart rate) determination circuitry are not active. Theuse of the physiological metric determination circuitry may be extendedto provide ambient light information for display brightness levelcontrol purposes. Where the optical physiological metric sensorcircuitry is designed to modify the light detector signal(s) to accountfor skin color or other factors, the display brightness level managementcircuitry may be configured to reconvert the ambient signal back to theraw ambient signal so as to provide a baseline signal for ambient lightdetermination. For example, PPG circuitry may be designed to applyscaling and/or gain biasing to the light detector signal(s) to accountfor different lighting conditions, skin tone, or the like; suchprocessing may effectively be reversed to get the raw ambient signal.

In addition to, or as an alternative to, using ambient light informationfor display brightness level management, certain embodiments disclosedherein provide for the use of such information for determining sunexposure, sleep detection, or the like. In certain embodiments, the PPGcircuitry may be configured to store ambient light data values duringoperation; such values may be used by the display brightness levelmanagement subsystem to determine display brightness level settings. Incertain embodiments, the PPG sensor runs at a 25 Hz sampling rate. Thedisplay brightness level management subsystem may store samples in acircular buffer.

Display Brightness Level Adjustment Processes

Certain embodiments disclosed herein provide processes for adjusting abrightness level setting of an electronic display, such as abacklighting setting, for a biometric monitoring device without the useof a dedicated front-side ambient light sensor. Reducing the intensityof display brightness in certain conditions may provide power savingsand/or reduce strain on the user's eyes when viewing the display inlow-light conditions. FIG. 16 is a flow diagram illustrating a process1600 for adjusting a brightness level setting of an electronic displayaccording to one or more embodiments. The process 1600 may provide powersavings and may be implemented as part of a power management scheme in abiometric monitoring device, such as a wrist-wearable biometricmonitoring device.

At block 1602, the process 1600 involves directing light from a lightsource of a wearable biometric monitoring device into tissue of a userduring a first time period. For example, the step of block 1602 mayinvolve activating one or more light sources associated with a backside(i.e., skin-facing when the biometric monitoring device is worn on auser's wrist) of the biometric monitoring device.

At block 1604, the process 1600 involves generating a first lightdetector signal using a skin-facing light detector, the first lightdetector signal indicating a first amount of light detected by the lightdetector during the first period. For example, the first light detectorsignal may be generated using a photodetector or other light detector,which may be a component of a physiological metric sensor module, suchas a module configured to implement optical components for determiningheart rate, blood oxygenation, or other physiological metric of theuser.

At block 1606, the process 1600 involves deactivating the light sourceduring a second period of time. For example, one or more light sourcesmay be pulsed or otherwise activated and deactivated, wherein the firstperiod of time corresponds with a period during which the lightsource(s) are active, while the second period of time corresponds to aperiod during which the light source(s) are deactivated, such that thephotodetector(s) do not detect light from the light sources during thesecond period of time.

At block 1608, the process 1600 involves generating a second lightdetector signal indicating a second amount of light detected by thelight detector during the second period. For example, the second lightdetector signal may be generated using the light detector utilized inconnection with step 1604. Because the light source(s) are not activatedduring the second period of time, the second light detector signal mayprovide a reading that indicates ambient light presence, as the lightdetected during the second period of time is not generally attributableto the light source(s).

At block 1610, the process 1600 involves generating a physiologicalmetric signal based at least in part on the first light detector signaland the second light detector signal. The physiological metric signalmay be generated at least in part by generating an ambient lightcancellation signal using the second light detector signal, which may beindicative of ambient light because it indicates detected light at atime when the light sources are not activated. The process 1600 mayinvolve cancelling ambient light in the first light detector signal bysubtracting out the ambient light indicated by the second light detectorsignal. Generating the ambient light cancellation signal can involveconditioning the second light detector signal to account for skin tonecharacteristics of the user, which may be determined in any suitable ordesirable way, such as through a calibration process or accessingprofile data. In certain embodiments, it may be necessary to at leastpartially reverse the conditioning of the second light detector signalto produce a raw ambient light signal, which may be used in determiningwhether or how to modify the display brightness level setting.

At block 1612, the process 1600 involves modifying a brightness settingof an electronic display based at least in part on the second lightdetector signal. For example, the brightness level may be modified basedon the second light detector signal, but not the first light detectorsignal. Because the second light detector signal may be indicative ofambient light, the utilization of such signal may be used to modify thebrightness of the display to account for ambient light conditions. Forexample, the process 1600 may involve determining whether an amplitudeof the raw ambient light signal is greater than a threshold. The ambientlight data from the second light detector signal may further be used todetermine other metrics, such as sun exposure. Ambient light datadetermined from the second light detector signal may be stored in abuffer (e.g., circular buffer) or other storage. When the amplitude ofthe second light detector signal is greater than a threshold, suchcondition may trigger modifying the brightness of the display to ahigher level. In certain embodiments, when the display brightness levelmanagement system determines that ambient lighting conditions are high,the high-level brightness level setting may be locked for a period oftime, such as until the display and/or biometric monitoring device ispowered down or placed in a sleep mode or low-power mode. Locking thebrightness level setting may help reduce or prevent unwanted flickeringor dimming of the display.

FIG. 17 is a block diagram illustrating an embodiment of a displaycontrol feedback system according to one or more embodiments. In someembodiments, a display control feedback system includes one or morehardware components, one or more software components and a communicationbus to interface between said hardware and software components. In someembodiments, a display control feedback system includes one or more LEDs1702 or another illumination device or light source. An example displaycontrol system may also include an output driver 1708 electricallyand/or communicatively coupled to LEDs 1702 and a timing controller1710. In some embodiments, the display control feedback system includesone or more light sensors 1704 (e.g., light detectors or devicesconfigured to detect light), electrically and/or communicatively coupledto a receiver/gain amplifier/filter chain block 1712. In someembodiments, light sensors 1704 and/or block 1712 include a transduceror another device to convert sensed readings (e.g., illumination) intoone or more electrical parameters (e.g., current or voltage). In someembodiments, the circuitry and/or functionality of block 1712 is splitacross more than one hardware component. For example, block 1712 mayrepresent in FIG. 17 a distinct hardware component for managingreception of detected light/illumination at the one or more lightsensors 1704, a distinct hardware component for managing the gain of anamplifier on the receive path of the light control feedback system, anda distinct hardware component for filtering a detectedlight/illumination value received by the one or more light sensors 1704.The display control feedback system may also include ananalog-to-digital converter (ADC) 1714, and a display 1706.

The display 1706, may be electrically and/or communicatively coupled toa display adjust block 1722. A display adjust block 1722 may beelectrically and/or communicatively coupled to a data processing block1720. Data processing block 1720 may be electrically and/orcommunicatively coupled to several software and/or hardware components,as shown in FIG. 17 . For example, data processing block 1720 may beelectrically and/or communicatively coupled to gain mode control/adjustblock 1716, data sampler block 1718, and timing controller 1710.

In some embodiments, a display control feedback system begins obtainingfeedback for a display system by driving one or more LEDs 1702 (e.g.,using output driver 1708). As described above, in some embodiments,light from a light source such as LEDs 1702, is transmitted into theskin and/or flesh of a user. In some embodiments, light is received byone or more light sensors 1704. The received light from light sensor(s)1704 is processed by receiver/gain amplifier/filter chain block 1712.For example, block 1712 may convert a level of determined illuminationinto an electrical parameter (e.g., voltage and/or current). In someembodiments, block 1712 includes one or more transducer blocks.Processed light/illumination information from the one or more lightsensors 1704 may be communicated to ADC 1714, which converts an analogrepresentation of the received light/illumination information into adigital representation passed to data sampler 1718 (e.g., through acommunication bus).

In some embodiments, one or more software components operate together toassess received light/illumination information initially received by theone or more light sensors 1704, and correspondingly make adjustments toone or more illumination parameters of LEDs 1702 (or of a light source),and/or adjust one or more reception parameters of the light sensor(s)1704. The one or more software components may be software modules orblocks residing in a non-transitory computer-readable storage medium, ormemory. As an example, the data processing block 1720 may receivesampled illumination information from data sampler 1718 and use thesampled illumination information to determine one or more physiologicalcharacteristics of the user. Examples of physiological characteristicsthat may be determined include, but are not limited to a user's skintone, level of melatonin in the skin, moisture level of the user's skinand proximity of the skin to the one or more light sensors 1704. In someembodiments, determining one or more physiological characteristics of auser allows for adjustment of light transmission (e.g., illuminationusing LEDs 1702) applied to the user's skin and/or flesh, and/oradjustment of light reception (e.g., illumination detection by lightsensor(s) 1704).

As shown in FIG. 17 , data processing block 1720 may be communicativelycoupled to gain mode control/adjust block 1716. Data processing block1720 may transmit sampled, processed illumination information receivedfrom the one or more light sensors 1704 and processed by block 1712 andADC 1714 and sampled by data sampler 1718, to gain mode control/adjustblock 1716. The gain mode control/adjust block 1716 may adjust one ormore illumination parameters through an electrical and/or communicativecoupling to output driver 1708. For example, gain mode control/adjustblock 1716 may instruct output driver 1708 to increase or decrease anapplied voltage corresponding to illumination intensity of the one ormore LEDs 1702. Additionally, gain mode control/adjust block 1716 mayreturn instructions to data processing block 1720, which may use theinstructions to adjust one or more illumination and/or receptionparameters, using timing controller 1710. In some embodiments, dataprocessing block 1720 instructs timing controller 1710 to adjust aduration of time for illumination of the one or more LEDs 1702 (e.g.,one or more light sources), and/or instructs timing controller 1710 toadjust a duration of time for reception of detected illumination/lightat the one or more light sensors 1704 (e.g., one or more lightdetectors). Although not shown in FIG. 17 , in some embodiments, gainmode control/adjust block 1716 is directly coupled electrically and/orcommunicatively to the receiver/gain amplifier/filter chain block 1712of the receive path. Whether coupled directly, or indirectly, gain modecontrol/adjust block 1716 may instruct block 1712 to adjust receiveramplifier gain settings (e.g., by adjusting one or more correspondingregister values). Alternatively, or additionally, gain modecontrol/adjust block 1716 may instruct block 1712 to adjust filtrationof the received illumination from light sensor(s) 1704, in the filterchain processing portion of block 1712.

In some embodiments, data processing block 1720 uses the result of afeedback-driven sampled, processed illumination reading to determine oneor more operational brightness modes of the display control feedbacksystem. For example, data processing block 1720 may determine that theuser is in an environment with an operational brightness mode of 3 outof 6. That is to say, that data processing block 1720 may rank an orderof operational brightness modes, based on detected levels ofillumination corresponding to each mode. In another example, dataprocessing block 1720 may qualitatively determine that the user is in anindoor lighting setting with dim lights. In some embodiments, thedetermined operational brightness mode is transmitted by data processingblock 1720 to display adjustment block 1722. An operational brightnessmode may correspond to a brightness level of display 1706. In someembodiments, display adjust block 1722 uses the operational brightnessmode determined by data processing unit 1720 to instruct display 1706 tochange a brightness level of display 1706. For example, if the user isin a relatively brightly lit environment, display adjustment block 1722may instruct display 1706 to increase brightness of display 1706, sothat the information on display 1706 is easier to read. In someembodiments, an operational brightness mode corresponds to additional oralternative parameters of display 1706 other than brightness alone, suchas but not limited to duration of brightness level and a rate ofincrease or decrease in illumination.

As described earlier, data processing block 1720 may determine anambient light level or value. In some embodiments, this determinedambient light level or value corresponds to an operational brightnessmode. For example, a measured or determined ambient light level may becompared to one or more threshold values (e.g., level of illumination),to determine a specific operational brightness mode. The determinedoperational brightness mode may then be used to adjust one or morebrightness parameters of display 1706 (e.g., brightness level, rate ofillumination). In some embodiments, the determined ambient light levelor value is determined with respect to determining or generating aphysiological metric (e.g., heart rate) of the user. Data processingblock 1720, display adjustment block 1722 and/or an additionalprocessing block (not shown) between blocks 1720 and 1722, may furtherprocess an ambient light level or value determined for generating thephysiological metric, for purposes of determining display adjustmentinformation. For example, the feedback loop described with respect toFIG. 17 may result in a first value for ambient light level, used by thedata processing block 1720 to determine a heart rate for the user. Thefirst ambient light level may further be processed by the dataprocessing block 1720 for purposes of assessing an operationalbrightness mode, into a second ambient light level (e.g., outdoors andsunny). The additionally processed ambient light level may be aquantitative value (e.g., 3/10) and/or a qualitative value (e.g., dim,indoors).

The one or more LEDs 1702, output driver 1708, timing controller 1710,receiver/gain amplifier/filter chain block 1712, one or more lightsensors 1704, display 1706, ADC 1714, gain mode control/adjust block1716, data processing block 1720, data sampler block 1718 and/or displayadjust block 1722 may have one or more characteristics of correspondingmodules, blocks, components or units described within this disclosure.

ADDITIONAL EMBODIMENTS

Depending on the embodiment, certain acts, events, or functions of anyof the processes or algorithms described herein can be performed in adifferent sequence, may be added, merged, or left out altogether. Thus,in certain embodiments, not all described acts or events are necessaryfor the practice of the processes. Moreover, in certain embodiments,acts or events may be performed concurrently, e.g., throughmulti-threaded processing, interrupt processing, or via multipleprocessors or processor cores, rather than sequentially.

Certain methods and/or processes described herein may be embodied in,and partially or fully automated via, software code modules executed byone or more general and/or special purpose computers. The word “module”refers to logic embodied in hardware and/or firmware, or to a collectionof software instructions, possibly having entry and exit points, writtenin a programming language, such as, for example, C or C++. A softwaremodule may be compiled and linked into an executable program, installedin a dynamically linked library, or may be written in an interpretedprogramming language such as, for example, BASIC, Perl, or Python. Itwill be appreciated that software modules may be callable from othermodules or from themselves, and/or may be invoked in response todetected events or interrupts. Software instructions may be embedded infirmware, such as an erasable programmable read-only memory (EPROM). Itwill be further appreciated that hardware modules may be comprised ofconnected logic units, such as gates and flip-flops, and/or may becomprised of programmable units, such as programmable gate arrays,application specific integrated circuits, and/or processors. The modulesdescribed herein are preferably implemented as software modules, but maybe represented in hardware and/or firmware. Moreover, although in someembodiments a module may be separately compiled, in other embodiments amodule may represent a subset of instructions of a separately compiledprogram, and may not have an interface available to other logicalprogram units.

In certain embodiments, code modules may be implemented and/or stored inany type of computer-readable medium or other computer storage device.In some systems, data (and/or metadata) input to the system, datagenerated by the system, and/or data used by the system can be stored inany type of computer data repository, such as a relational databaseand/or flat file system. Any of the systems, methods, and processesdescribed herein may include an interface configured to permitinteraction with patients, health care practitioners, administrators,other systems, components, programs, and so forth.

Embodiments of the disclosed systems and methods can be used and/orimplemented with local and/or remote devices, components, and/ormodules. The term “remote” may include devices, components, and/ormodules not stored locally, for example, not accessible via a local bus.Thus, a remote device may include a device which is physically locatedin the same room and connected via a device such as a switch or a localarea network. In other situations, a remote device may also be locatedin a separate geographic area, such as, for example, in a differentlocation, building, city, country, and so forth.

Conditional language used herein, such as, among others, “can,” “could,”“might,” “may,” “e.g.,” and the like, unless specifically statedotherwise, or otherwise understood within the context as used, isintended in its ordinary sense and is generally intended to convey thatcertain embodiments include, while other embodiments do not include,certain features, elements and/or steps. Thus, such conditional languageis not generally intended to imply that features, elements and/or stepsare in any way required for one or more embodiments or that one or moreembodiments necessarily include logic for deciding, with or withoutauthor input or prompting, whether these features, elements and/or stepsare included or are to be performed in any particular embodiment. Theterms “comprising,” “including,” “having,” and the like are synonymous,are used in their ordinary sense, and are used inclusively, in anopen-ended fashion, and do not exclude additional elements, features,acts, operations, and so forth. Also, the term “or” is used in itsinclusive sense (and not in its exclusive sense) so that when used, forexample, to connect a list of elements, the term “or” means one, some,or all of the elements in the list. Conjunctive language such as thephrase “at least one of X, Y and Z,” unless specifically statedotherwise, is understood with the context as used in general to conveythat an item, term, element, etc. may be either X, Y or Z. Thus, suchconjunctive language is not generally intended to imply that certainembodiments require at least one of X, at least one of Y and at leastone of Z to each be present.

Reference throughout this specification to “certain embodiments” or “anembodiment” means that a particular feature, structure or characteristicdescribed in connection with the embodiment is included in at least someembodiments. Thus, appearances of the phrases “in some embodiments” or“in an embodiment” in various places throughout this specification arenot necessarily all referring to the same embodiment and may refer toone or more of the same or different embodiments. Furthermore, theparticular features, structures or characteristics can be combined inany suitable manner, as would be apparent to one of ordinary skill inthe art from this disclosure, in one or more embodiments.

It should be appreciated that in the above description of embodiments,various features are sometimes grouped together in a single embodiment,figure, or description thereof for the purpose of streamlining thedisclosure and aiding in the understanding of one or more of the variousinventive aspects. This method of disclosure, however, is not to beinterpreted as reflecting an intention that any claim require morefeatures than are expressly recited in that claim. Moreover, anycomponents, features, or steps illustrated and/or described in aparticular embodiment herein can be applied to or used with any otherembodiment(s). Further, no component, feature, step, or group ofcomponents, features, or steps are necessary or indispensable for eachembodiment. Thus, it is intended that the scope of the inventions hereindisclosed and claimed below should not be limited by the particularembodiments described above, but should be determined only by a fairreading of the claims that follow.

What is claimed is:
 1. A wearable computing device, comprising: an electronic display with a configurable brightness level setting; a physiological metric sensor system comprising, a light source and a light detector, the light source positioned on a wrist-side of the wearable computing device to direct light into tissue of a user when the user is wearing the wearable computing device on a wrist of the user, the light detector positioned on the wrist-side of the wearable computing device adjacent to the light source to detect light from the light source that reflects back from the user; and control circuitry configured to: turn the light source on and off; collect data via the light detector at least while the light source is off to provide information for evaluation relative to an ambient light level; and modify the configurable brightness level setting of the electronic display based at least in part on the ambient light level.
 2. The wearable computing device of claim 1, wherein the control circuitry is further configured to: determine, one or more physiological characteristics of the user; adjust one or more illumination parameters of the light source based on the determined one or more physiological characteristics; and adjust one or more reception parameters of the light detector based on the determined one or more physiological characteristics.
 3. The wearable computing device of claim 2, wherein the control circuitry is further configured to adjust the one or more reception parameters of the light detector before generating a second light detector signal.
 4. The wearable computing device of claim 2, wherein the control circuitry is further configured to adjust the one or more illumination parameters and to adjust the one or more reception parameters before activating the light source during a first period.
 5. The wearable computing device of claim 1, wherein the control circuitry is configured to generate light while the light source is turned on using a transimpedance amplifier coupled to sample-and-hold circuitry.
 6. The wearable computing device of claim 1, wherein said modifying the configurable brightness level setting comprises changing the configurable brightness level setting associated with a first mode to a second mode.
 7. The wearable computing device of claim 6, wherein the first mode corresponds to an outdoor lighting condition and the second mode corresponds to an indoor lighting condition.
 8. The wearable computing device of claim 6, wherein the first mode corresponds to an indoor lighting condition and the second mode corresponds to an outdoor lighting condition.
 9. The wearable computing device of claim 6, wherein the second mode is associated with a relatively higher brightness level compared to the first mode.
 10. The wearable computing device of claim 6, wherein the second mode is associated with a relatively lower brightness level compared to the first mode.
 11. The wearable computing device of claim 6, wherein the control circuitry is further configured to lock the configurable brightness level setting of the electronic display in the second mode until the electronic display is powered down.
 12. The wearable computing device of claim 6, wherein the first mode and the second mode form a subset of a group of three or more operational brightness modes for the electronic display.
 13. The wearable computing device of claim 1, wherein the light source comprises a plurality of LED light sources.
 14. A method of managing power in a wearable computing device, the wearable computing device having an electronic display with a configurable brightness level setting, a light source, and a light detector, the light source positioned on a wrist-side of the wearable computing device to direct light into tissue of a user when the user is wearing the wearable computing device on a wrist of the user, the light detector positioned on the wrist-side of the wearable computing device adjacent to the light source to detect light from the light source that reflects back from the user, the method comprising: placing the wearable computing device on a wrist of a user; turning the light source on and off, collecting data via the light detector at least while the light source is off to provide information for evaluation relative to an ambient light level; and modifying the configurable brightness level setting of the electronic display based at least in part on the ambient light level.
 15. The method of claim 14, further comprising determining an amount of sun exposure of the user based at least in part on the data collected via the light detector at least while the light source is off.
 16. The method of claim 14, further comprising storing a value associated with the data collected via the light detector at least while the light source is off in a circular buffer.
 17. The method of claim 14, further comprising determining whether an amplitude of a light detector signal representative of the data collected via the light detector at least while the light source is off is greater than a threshold.
 18. The method of claim 14, wherein said modifying the configurable brightness level of the electronic display comprises adjusting the configurable brightness level from a first state to a second state.
 19. The method of claim 18, wherein the first state corresponds to a low-light mode and the second state corresponds to a high-light mode. 